diff --git a/docs/openapi/parameters.yaml b/docs/openapi/parameters.yaml
index cb72766072..de91c9a753 100644
--- a/docs/openapi/parameters.yaml
+++ b/docs/openapi/parameters.yaml
@@ -401,6 +401,21 @@ xPromiseToken:
     type: string
   example: eyJhbGciOiJSUzI1NiIs...
 
+locale:
+  name: locale
+  description: |
+    Locale code in underscore form (e.g. `fr_fr`, `ja_jp`, `de_de`).
+    When provided and a translation exists, localizable fields (`title`, `description` on
+    opportunities; AI-generated fields inside `data` on suggestions) are replaced by the
+    stored translation. Falls back to the original English value when the locale is absent
+    or no translation has been stored yet for that locale.
+  in: query
+  required: false
+  schema:
+    type: string
+    pattern: '^[a-z]{2}_[a-z]{2}$'
+    example: fr_fr
+
 suggestionView:
   name: view
   description: |
diff --git a/docs/openapi/site-opportunities.yaml b/docs/openapi/site-opportunities.yaml
index 6a5368e0c1..1cacde83e7 100644
--- a/docs/openapi/site-opportunities.yaml
+++ b/docs/openapi/site-opportunities.yaml
@@ -1,6 +1,7 @@
 site-opportunities:
   parameters:
     - $ref: './parameters.yaml#/siteId'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunities
     summary: |
@@ -71,6 +72,7 @@ site-opportunities-by-status:
       required: true
       schema:
         type: string
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitiesByStatus
     summary: |
@@ -103,6 +105,7 @@ site-opportunity:
   parameters:
     - $ref: './parameters.yaml#/siteId'
     - $ref: './parameters.yaml#/opportunityId'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunity
     summary: |
@@ -197,6 +200,7 @@ site-opportunity-suggestions:
     - $ref: './parameters.yaml#/opportunityId'
     - $ref: './parameters.yaml#/suggestionView'
     - $ref: './parameters.yaml#/suggestionStatus'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestions
     summary: |
@@ -278,6 +282,7 @@ site-opportunity-suggestions-by-status:
       schema:
         type: string
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestionsByStatus
     summary: |
@@ -314,6 +319,7 @@ site-opportunity-suggestions-paged:
     - $ref: './parameters.yaml#/opportunityId'
     - $ref: './parameters.yaml#/limit'
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestionsPaged
     summary: |
@@ -353,6 +359,7 @@ site-opportunity-suggestions-paged-with-cursor:
     - $ref: './parameters.yaml#/limit'
     - $ref: './parameters.yaml#/cursor'
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestionsPagedWithCursor
     summary: |
@@ -396,6 +403,7 @@ site-opportunity-suggestions-by-status-paged:
         type: string
     - $ref: './parameters.yaml#/limit'
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestionsByStatusPaged
     summary: |
@@ -439,6 +447,7 @@ site-opportunity-suggestions-by-status-paged-with-cursor:
     - $ref: './parameters.yaml#/limit'
     - $ref: './parameters.yaml#/cursor'
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestionsByStatusPagedWithCursor
     summary: |
@@ -1082,6 +1091,7 @@ site-opportunity-suggestion:
     - $ref: './parameters.yaml#/opportunityId'
     - $ref: './parameters.yaml#/suggestionId'
     - $ref: './parameters.yaml#/suggestionView'
+    - $ref: './parameters.yaml#/locale'
   get:
     operationId: getSiteOpportunitySuggestion
     summary: |
diff --git a/src/controllers/opportunities.js b/src/controllers/opportunities.js
index 27b0c87632..ad90a558b6 100644
--- a/src/controllers/opportunities.js
+++ b/src/controllers/opportunities.js
@@ -26,6 +26,7 @@ import {
   isValidUUID,
 } from '@adobe/spacecat-shared-utils';
 import { OpportunityDto } from '../dto/opportunity.js';
+import { isValidLocale } from '../utils/validations.js';
 import AccessControlUtil from '../support/access-control-util.js';
 import { grantSuggestionsForOpportunity } from '../support/grant-suggestions-handler.js';
 import { getIsSummitPlgEnabled } from '../support/utils.js';
@@ -96,6 +97,11 @@ function OpportunitiesController(ctx) {
    */
   const getAllForSite = async (context) => {
     const siteId = context.params?.siteId;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -111,7 +117,7 @@ function OpportunitiesController(ctx) {
 
     const allOpptys = await Opportunity.allBySiteId(siteId);
     const opptys = (await filterForSummitPlg(site, allOpptys, context))
-      .map((oppty) => OpportunityDto.toJSON(oppty));
+      .map((oppty) => OpportunityDto.toJSON(oppty, locale));
 
     return ok(opptys);
   };
@@ -124,6 +130,11 @@ function OpportunitiesController(ctx) {
   const getByStatus = async (context) => {
     const siteId = context.params?.siteId;
     const status = context.params?.status;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -142,7 +153,7 @@ function OpportunitiesController(ctx) {
 
     const allOpptys = await Opportunity.allBySiteIdAndStatus(siteId, status);
     const opptys = (await filterForSummitPlg(site, allOpptys, context))
-      .map((oppty) => OpportunityDto.toJSON(oppty));
+      .map((oppty) => OpportunityDto.toJSON(oppty, locale));
 
     return ok(opptys);
   };
@@ -155,6 +166,11 @@ function OpportunitiesController(ctx) {
   const getByID = async (context) => {
     const siteId = context.params?.siteId;
     const opptyId = context.params?.opportunityId;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -184,7 +200,7 @@ function OpportunitiesController(ctx) {
         ctx.log?.warn?.('Grant suggestions handler failed', err?.message ?? err);
       }
     }
-    return ok(OpportunityDto.toJSON(oppty));
+    return ok(OpportunityDto.toJSON(oppty, locale));
   };
 
   /**
diff --git a/src/controllers/suggestions.js b/src/controllers/suggestions.js
index 322fa4e917..4d3aab2405 100644
--- a/src/controllers/suggestions.js
+++ b/src/controllers/suggestions.js
@@ -32,6 +32,7 @@ import { Suggestion as SuggestionModel, GeoExperiment as GeoExperimentModel } fr
 import TokowakaClient from '@adobe/spacecat-shared-tokowaka-client';
 import DrsClient, { EXPERIMENT_PHASES } from '@adobe/spacecat-shared-drs-client';
 import { SuggestionDto, SUGGESTION_VIEWS, SUGGESTION_SKIP_REASONS } from '../dto/suggestion.js';
+import { isValidLocale } from '../utils/validations.js';
 import {
   getScheduleParams,
   buildExperimentMetadata,
@@ -301,6 +302,11 @@ function SuggestionsController(ctx, sqs, env) {
     const opptyId = context.params?.opportunityId;
     const viewParam = context.data?.view;
     const statusParam = context.data?.status;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -357,7 +363,7 @@ function SuggestionsController(ctx, sqs, env) {
     }
     const grantedEntities = await filterByGrantStatus(site, suggestionEntities, context);
     const suggestions = grantedEntities.map(
-      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity),
+      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity, locale),
     );
     return ok(suggestions);
   };
@@ -376,6 +382,11 @@ function SuggestionsController(ctx, sqs, env) {
     const limit = parseInt(context.params?.limit, 10) || DEFAULT_PAGE_SIZE;
     const cursor = context.params?.cursor || null;
     const viewParam = context.data?.view;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -418,7 +429,7 @@ function SuggestionsController(ctx, sqs, env) {
     }
     const grantedEntities = await filterByGrantStatus(site, suggestionEntities, context);
     const suggestions = grantedEntities.map(
-      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity),
+      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity, locale),
     );
 
     return ok({
@@ -441,6 +452,11 @@ function SuggestionsController(ctx, sqs, env) {
     const opptyId = context.params?.opportunityId;
     const status = context.params?.status || undefined;
     const viewParam = context.data?.view;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -476,7 +492,7 @@ function SuggestionsController(ctx, sqs, env) {
     }
     const grantedEntities = await filterByGrantStatus(site, suggestionEntities, context);
     const suggestions = grantedEntities.map(
-      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity),
+      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity, locale),
     );
     return ok(suggestions);
   };
@@ -493,6 +509,11 @@ function SuggestionsController(ctx, sqs, env) {
     const limit = parseInt(context.params?.limit, 10) || DEFAULT_PAGE_SIZE;
     const cursor = context.params?.cursor || null;
     const viewParam = context.data?.view;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -537,7 +558,7 @@ function SuggestionsController(ctx, sqs, env) {
     }
     const grantedEntities = await filterByGrantStatus(site, suggestionEntities, context);
     const suggestions = grantedEntities.map(
-      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity),
+      (sugg) => SuggestionDto.toJSON(sugg, view, opportunity, locale),
     );
     return ok({
       suggestions,
@@ -559,6 +580,11 @@ function SuggestionsController(ctx, sqs, env) {
     const opptyId = context.params?.opportunityId || undefined;
     const suggestionId = context.params?.suggestionId || undefined;
     const viewParam = context.data?.view;
+    const locale = context.data?.locale ?? null;
+
+    if (!isValidLocale(locale)) {
+      return badRequest('Invalid locale format');
+    }
 
     if (!isValidUUID(siteId)) {
       return badRequest('Site ID required');
@@ -598,7 +624,7 @@ function SuggestionsController(ctx, sqs, env) {
       && !(await SuggestionGrant.isSuggestionGranted(suggestion.getId()))) {
       return notFound('Suggestion not found');
     }
-    return ok(SuggestionDto.toJSON(suggestion, view, opportunity));
+    return ok(SuggestionDto.toJSON(suggestion, view, opportunity, locale));
   };
 
   /**
diff --git a/src/dto/opportunity.js b/src/dto/opportunity.js
index 64e16df519..ba6c0836c1 100644
--- a/src/dto/opportunity.js
+++ b/src/dto/opportunity.js
@@ -21,7 +21,15 @@ export const OpportunityDto = {
    * that must only appear in the brand-scoped endpoint response, added by the brand
    * controller directly. Including them here would expose brand UUIDs on shared sites
    * to users who have site access but not brand access.
+   *
+   * Translations for `title` and `description` are stored by audit workers in
+   * `opportunity.data.i18n` as a map of locale → { title, description }.
+   * When `locale` is supplied the matching translation is promoted to the top-level
+   * fields and `data.i18n` is stripped from the response so the shape stays stable.
+   * Falls back to the original English values when the locale is absent or not found.
+   *
    * @param {Readonly<Opportunity>} oppty - Opportunity object.
+   * @param {string|null} [locale] - Optional locale code (e.g. 'fr_fr', 'ja_jp').
    * @returns {{
     * id: string,
     * siteId: string,
@@ -40,22 +48,44 @@ export const OpportunityDto = {
     * lastAuditedAt: date
     * }} JSON object.
    */
-  toJSON: (oppty) => ({
-    id: oppty.getId(),
-    siteId: oppty.getSiteId(),
-    auditId: oppty.getAuditId(),
-    runbook: oppty.getRunbook(),
-    type: oppty.getType(),
-    data: oppty.getData(),
-    origin: oppty.getOrigin(),
-    title: oppty.getTitle(),
-    description: oppty.getDescription(),
-    guidance: oppty.getGuidance(),
-    tags: oppty.getTags(),
-    status: oppty.getStatus(),
-    createdAt: oppty.getCreatedAt(),
-    updatedAt: oppty.getUpdatedAt(),
-    updatedBy: oppty.getUpdatedBy(),
-    lastAuditedAt: oppty.getLastAuditedAt(),
-  }),
+  toJSON: (oppty, locale = null) => {
+    const rawData = oppty.getData();
+    const data = rawData ? (() => {
+      // eslint-disable-next-line no-unused-vars
+      const { i18n, ...rest } = rawData;
+      return rest;
+    })() : null;
+
+    let title = oppty.getTitle();
+    let description = oppty.getDescription();
+
+    if (locale && rawData?.i18n?.[locale]) {
+      const localized = rawData.i18n[locale];
+      if (localized.title != null) {
+        title = localized.title;
+      }
+      if (localized.description != null) {
+        description = localized.description;
+      }
+    }
+
+    return {
+      id: oppty.getId(),
+      siteId: oppty.getSiteId(),
+      auditId: oppty.getAuditId(),
+      runbook: oppty.getRunbook(),
+      type: oppty.getType(),
+      data,
+      origin: oppty.getOrigin(),
+      title,
+      description,
+      guidance: oppty.getGuidance(),
+      tags: oppty.getTags(),
+      status: oppty.getStatus(),
+      createdAt: oppty.getCreatedAt(),
+      updatedAt: oppty.getUpdatedAt(),
+      updatedBy: oppty.getUpdatedBy(),
+      lastAuditedAt: oppty.getLastAuditedAt(),
+    };
+  },
 };
diff --git a/src/dto/suggestion.js b/src/dto/suggestion.js
index 3d67955768..e4858f9d7c 100644
--- a/src/dto/suggestion.js
+++ b/src/dto/suggestion.js
@@ -19,6 +19,20 @@ import { Suggestion } from '@adobe/spacecat-shared-data-access';
  */
 export const SUGGESTION_VIEWS = ['minimal', 'summary', 'full'];
 
+/**
+ * Supported localizable fields that can be translated for suggestions.
+ * @type {string[]}
+ */
+export const ALLOWED_I18N_FIELDS = [
+  'title',
+  'description',
+  'rationale',
+  'aiRationale',
+  'aiSuggestion',
+  'actionItems',
+  'persona',
+];
+
 /**
  * Valid skip reasons when a suggestion is marked as SKIPPED.
  * @type {string[]}
@@ -64,15 +78,39 @@ const extractMinimalData = (data, opportunityType) => {
 export const SuggestionDto = {
   /**
    * Converts a Suggestion object into a JSON object with optional projection.
+   *
+   * Translations for AI-generated fields (title, rationale, description, etc.) are stored by
+   * audit workers in `suggestion.data.i18n` as a map of locale → { field: value, ... }.
+   * When `locale` is supplied the matching translation is merged on top of `data` and
+   * `data.i18n` is stripped so the response shape stays stable.
+   * Falls back to the original English values when the locale is absent or not found.
+   *
    * @param {Readonly<Suggestion>} suggestion - Suggestion object.
    * @param {string} [view='full'] - Projection view: 'minimal', 'summary', or 'full'.
    * @param {object} [opportunity] - Optional opportunity entity for type-specific filtering.
+   * @param {string|null} [locale] - Optional locale code (e.g. 'fr_fr', 'ja_jp').
    * @returns {object} JSON object with fields based on the selected view.
    */
-  toJSON: (suggestion, view = 'full', opportunity = null) => {
-    const data = suggestion.getData();
+  toJSON: (suggestion, view = 'full', opportunity = null, locale = null) => {
+    const rawData = suggestion.getData();
     const opportunityType = opportunity?.getType() || null;
 
+    // Apply locale projection and strip the internal i18n key from the response
+    // eslint-disable-next-line no-unused-vars
+    const { i18n, ...baseData } = rawData ?? {};
+    let data = baseData;
+
+    if (locale && i18n?.[locale]) {
+      const localized = i18n[locale];
+      const filteredLocalized = {};
+      for (const field of ALLOWED_I18N_FIELDS) {
+        if (localized[field] != null) {
+          filteredLocalized[field] = localized[field];
+        }
+      }
+      data = { ...baseData, ...filteredLocalized };
+    }
+
     const skipReason = suggestion.getSkipReason?.();
     const skipDetail = suggestion.getSkipDetail?.();
     const skipFields = {};
diff --git a/src/utils/validations.js b/src/utils/validations.js
index effc1d5231..dd040f6141 100644
--- a/src/utils/validations.js
+++ b/src/utils/validations.js
@@ -47,8 +47,22 @@ function checkBodySize(data, maxSize) {
   return true;
 }
 
+/**
+ * Validates if the locale is a valid locale code (e.g. 'fr_fr').
+ *
+ * @param {string} locale - The locale code.
+ * @returns {boolean} true if the locale is valid, false otherwise.
+ */
+function isValidLocale(locale) {
+  if (locale === undefined || locale === null) {
+    return true;
+  }
+  return typeof locale === 'string' && /^[a-z]{2}_[a-z]{2}$/.test(locale);
+}
+
 export {
   MAX_BODY_SIZE,
   validateRepoUrl,
   checkBodySize,
+  isValidLocale,
 };
diff --git a/test/controllers/opportunities.test.js b/test/controllers/opportunities.test.js
index 2f927185b9..6c31a8ae36 100644
--- a/test/controllers/opportunities.test.js
+++ b/test/controllers/opportunities.test.js
@@ -318,6 +318,43 @@ describe('Opportunities Controller', () => {
     expect(opportunity).to.have.property('id', OPPORTUNITY_ID);
   });
 
+  describe('locale validation', () => {
+    const invalidLocaleContext = { data: { locale: 'fr-FR' } };
+
+    it('getAllForSite returns bad request for invalid locale', async () => {
+      const response = await opportunitiesController.getAllForSite({
+        params: { siteId: SITE_ID },
+        ...invalidLocaleContext,
+      });
+      expect(mockOpportunityDataAccess.Opportunity.allBySiteId.called).to.be.false;
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getByStatus returns bad request for invalid locale', async () => {
+      const response = await opportunitiesController.getByStatus({
+        params: { siteId: SITE_ID, status: 'NEW' },
+        ...invalidLocaleContext,
+      });
+      expect(mockOpportunityDataAccess.Opportunity.allBySiteIdAndStatus.called).to.be.false;
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getByID returns bad request for invalid locale', async () => {
+      const response = await opportunitiesController.getByID({
+        params: { siteId: SITE_ID, opportunityId: OPPORTUNITY_ID },
+        ...invalidLocaleContext,
+      });
+      expect(mockOpportunityDataAccess.Opportunity.findById.called).to.be.false;
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+  });
+
   it('gets all opportunities for a site by status returns bad request if no site ID is passed', async () => {
     const response = await opportunitiesController.getByStatus({ params: {} });
     expect(mockOpportunityDataAccess.Opportunity.allBySiteIdAndStatus.calledOnce).to.be.false;
diff --git a/test/controllers/suggestions.test.js b/test/controllers/suggestions.test.js
index 611f7e96d5..3ce36f1952 100644
--- a/test/controllers/suggestions.test.js
+++ b/test/controllers/suggestions.test.js
@@ -562,6 +562,72 @@ describe('Suggestions Controller', () => {
     expect(suggestions[0]).to.have.property('opportunityId', OPPORTUNITY_ID);
   });
 
+  describe('locale validation', () => {
+    const invalidLocaleContext = { data: { locale: 'fr-FR' } };
+    const baseParams = {
+      params: {
+        siteId: SITE_ID,
+        opportunityId: OPPORTUNITY_ID,
+      },
+      ...context,
+    };
+
+    it('getAllForOpportunity returns bad request for invalid locale', async () => {
+      const response = await suggestionsController.getAllForOpportunity({
+        ...baseParams,
+        ...invalidLocaleContext,
+      });
+      expect(mockSuggestionDataAccess.Suggestion.allByOpportunityId.called).to.be.false;
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getAllForOpportunityPaged returns bad request for invalid locale', async () => {
+      const response = await suggestionsController.getAllForOpportunityPaged({
+        ...baseParams,
+        params: { ...baseParams.params, limit: '10' },
+        ...invalidLocaleContext,
+      });
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getByStatus returns bad request for invalid locale', async () => {
+      const response = await suggestionsController.getByStatus({
+        ...baseParams,
+        params: { ...baseParams.params, status: 'NEW' },
+        ...invalidLocaleContext,
+      });
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getByStatusPaged returns bad request for invalid locale', async () => {
+      const response = await suggestionsController.getByStatusPaged({
+        ...baseParams,
+        params: { ...baseParams.params, status: 'NEW', limit: '10' },
+        ...invalidLocaleContext,
+      });
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+
+    it('getByID returns bad request for invalid locale', async () => {
+      const response = await suggestionsController.getByID({
+        ...baseParams,
+        params: { ...baseParams.params, suggestionId: SUGGESTION_IDS[0] },
+        ...invalidLocaleContext,
+      });
+      expect(response.status).to.equal(400);
+      const error = await response.json();
+      expect(error).to.have.property('message', 'Invalid locale format');
+    });
+  });
+
   it('returns all suggestions when grant filtering throws an error', async () => {
     mockSuggestionGrant.splitSuggestionsByGrantStatus.rejects(new Error('db failure'));
     const ControllerWithSummitPlg = await esmock('../../src/controllers/suggestions.js', {
diff --git a/test/dto/opportunity.test.js b/test/dto/opportunity.test.js
new file mode 100644
index 0000000000..c93bfaba70
--- /dev/null
+++ b/test/dto/opportunity.test.js
@@ -0,0 +1,159 @@
+/*
+ * Copyright 2026 Adobe. All rights reserved.
+ * This file is licensed to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+ * OF ANY KIND, either express or implied. See the License for the specific language
+ * governing permissions and limitations under the License.
+ */
+
+import { expect } from 'chai';
+import { OpportunityDto } from '../../src/dto/opportunity.js';
+
+describe('OpportunityDto', () => {
+  const createMockOppty = (dataOverrides = {}, opptyOverrides = {}) => ({
+    getId: () => 'oppty-id-123',
+    getSiteId: () => 'site-id-456',
+    getAuditId: () => 'audit-id-789',
+    getRunbook: () => 'http://runbook.url',
+    getType: () => 'youtube-analysis',
+    getData: () => ({ someField: 'value', ...dataOverrides }),
+    getOrigin: () => 'ESS_OPS',
+    getTitle: () => opptyOverrides.title ?? 'English title',
+    getDescription: () => opptyOverrides.description ?? 'English description',
+    getGuidance: () => ({ steps: [] }),
+    getTags: () => ['video content'],
+    getStatus: () => 'NEW',
+    getCreatedAt: () => '2025-01-01T00:00:00.000Z',
+    getUpdatedAt: () => '2025-01-02T00:00:00.000Z',
+    getUpdatedBy: () => 'system',
+    getLastAuditedAt: () => '2025-01-01T00:00:00.000Z',
+  });
+
+  describe('toJSON', () => {
+    it('returns all standard fields without locale', () => {
+      const oppty = createMockOppty();
+
+      const json = OpportunityDto.toJSON(oppty);
+
+      expect(json).to.have.property('id', 'oppty-id-123');
+      expect(json).to.have.property('siteId', 'site-id-456');
+      expect(json).to.have.property('title', 'English title');
+      expect(json).to.have.property('description', 'English description');
+      expect(json).to.have.property('data');
+      expect(json.data).to.have.property('someField', 'value');
+    });
+
+    describe('locale projection', () => {
+      it('returns original English when no locale is provided', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: 'Titre français', description: 'Description française' } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty);
+
+        expect(json.title).to.equal('English title');
+        expect(json.description).to.equal('English description');
+        expect(json.data).to.not.have.property('i18n');
+      });
+
+      it('promotes locale-specific title and description when locale matches', () => {
+        const oppty = createMockOppty({
+          i18n: {
+            fr_fr: { title: 'Titre français', description: 'Description française' },
+          },
+        });
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('Titre français');
+        expect(json.description).to.equal('Description française');
+        expect(json.data).to.not.have.property('i18n');
+        expect(json.data).to.have.property('someField', 'value');
+      });
+
+      it('falls back to English when locale has no stored translation', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: 'Titre français', description: 'Description française' } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty, 'ja_jp');
+
+        expect(json.title).to.equal('English title');
+        expect(json.description).to.equal('English description');
+      });
+
+      it('promotes only the fields present in the locale translation', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('Titre français');
+        expect(json.description).to.equal('English description');
+      });
+
+      it('promotes empty-string translations (intentional blank override)', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: '', description: '' } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('');
+        expect(json.description).to.equal('');
+      });
+
+      it('falls back to English when locale field is null', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: 'Titre français', description: null } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('Titre français');
+        expect(json.description).to.equal('English description');
+      });
+
+      it('strips i18n key from data even without locale param', () => {
+        const oppty = createMockOppty({
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = OpportunityDto.toJSON(oppty);
+
+        expect(json.data).to.not.have.property('i18n');
+        expect(json.data).to.have.property('someField', 'value');
+      });
+
+      it('handles getData returning null gracefully', () => {
+        const oppty = {
+          ...createMockOppty(),
+          getData: () => null,
+        };
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('English title');
+        expect(json.description).to.equal('English description');
+        expect(json.data).to.be.null;
+      });
+
+      it('handles getData returning empty object gracefully', () => {
+        const oppty = {
+          ...createMockOppty(),
+          getData: () => ({}),
+        };
+
+        const json = OpportunityDto.toJSON(oppty, 'fr_fr');
+
+        expect(json.title).to.equal('English title');
+        expect(json.data).to.deep.equal({});
+      });
+    });
+  });
+});
diff --git a/test/dto/suggestion.test.js b/test/dto/suggestion.test.js
index b3670f06a6..e5c7a4f3d7 100644
--- a/test/dto/suggestion.test.js
+++ b/test/dto/suggestion.test.js
@@ -12,7 +12,12 @@
 
 import { expect } from 'chai';
 
-import { SuggestionDto, SUGGESTION_VIEWS, SUGGESTION_SKIP_REASONS } from '../../src/dto/suggestion.js';
+import {
+  SuggestionDto,
+  SUGGESTION_VIEWS,
+  SUGGESTION_SKIP_REASONS,
+  ALLOWED_I18N_FIELDS,
+} from '../../src/dto/suggestion.js';
 
 describe('Suggestion DTO', () => {
   const createMockSuggestion = (dataOverrides = {}, suggestionOverrides = {}) => ({
@@ -36,6 +41,20 @@ describe('Suggestion DTO', () => {
     });
   });
 
+  describe('ALLOWED_I18N_FIELDS', () => {
+    it('exports the supported localizable suggestion fields', () => {
+      expect(ALLOWED_I18N_FIELDS).to.deep.equal([
+        'title',
+        'description',
+        'rationale',
+        'aiRationale',
+        'aiSuggestion',
+        'actionItems',
+        'persona',
+      ]);
+    });
+  });
+
   describe('SUGGESTION_SKIP_REASONS', () => {
     it('exports valid skip reason enum values from shared-data-access', () => {
       expect(SUGGESTION_SKIP_REASONS).to.be.an('array').that.is.not.empty;
@@ -619,5 +638,117 @@ describe('Suggestion DTO', () => {
         });
       });
     });
+
+    describe('locale projection', () => {
+      it('returns original English data when no locale is provided', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, null);
+
+        expect(json.data).to.have.property('title', 'English title');
+        expect(json.data).to.not.have.property('i18n');
+      });
+
+      it('promotes locale-specific fields when locale matches', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          rationale: 'English rationale',
+          i18n: {
+            fr_fr: { title: 'Titre français', rationale: 'Justification française' },
+          },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'fr_fr');
+
+        expect(json.data).to.have.property('title', 'Titre français');
+        expect(json.data).to.have.property('rationale', 'Justification française');
+        expect(json.data).to.not.have.property('i18n');
+      });
+
+      it('falls back to English when locale has no stored translation', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'ja_jp');
+
+        expect(json.data).to.have.property('title', 'English title');
+        expect(json.data).to.not.have.property('i18n');
+      });
+
+      it('strips i18n key even when locale is not provided', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full');
+
+        expect(json.data).to.not.have.property('i18n');
+      });
+
+      it('preserves non-translated fields alongside translated ones', () => {
+        const suggestion = createMockSuggestion({
+          url: 'https://example.com/page',
+          title: 'English title',
+          i18n: { fr_fr: { title: 'Titre français' } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'fr_fr');
+
+        expect(json.data).to.have.property('url', 'https://example.com/page');
+        expect(json.data).to.have.property('title', 'Titre français');
+      });
+
+      it('promotes empty-string translations for allowed fields', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          rationale: 'English rationale',
+          i18n: { fr_fr: { title: '', rationale: '' } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'fr_fr');
+
+        expect(json.data).to.have.property('title', '');
+        expect(json.data).to.have.property('rationale', '');
+      });
+
+      it('falls back to English when locale field is null', () => {
+        const suggestion = createMockSuggestion({
+          title: 'English title',
+          rationale: 'English rationale',
+          i18n: { fr_fr: { title: 'Titre français', rationale: null } },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'fr_fr');
+
+        expect(json.data).to.have.property('title', 'Titre français');
+        expect(json.data).to.have.property('rationale', 'English rationale');
+      });
+
+      it('ignores disallowed fields in locale translations', () => {
+        const suggestion = createMockSuggestion({
+          url: 'https://example.com/page',
+          title: 'English title',
+          i18n: {
+            fr_fr: {
+              title: 'Titre français',
+              url: 'https://example.com/fr-page',
+              customField: 'should not appear',
+            },
+          },
+        });
+
+        const json = SuggestionDto.toJSON(suggestion, 'full', null, 'fr_fr');
+
+        expect(json.data).to.have.property('title', 'Titre français');
+        expect(json.data).to.have.property('url', 'https://example.com/page');
+        expect(json.data).to.not.have.property('customField');
+      });
+    });
   });
 });
diff --git a/test/it/postgres/seed-data/opportunities.js b/test/it/postgres/seed-data/opportunities.js
index d8d5b50ad1..c3d1b1c1be 100644
--- a/test/it/postgres/seed-data/opportunities.js
+++ b/test/it/postgres/seed-data/opportunities.js
@@ -28,7 +28,17 @@ export const opportunities = [
     title: 'Fix CWV issues',
     description: 'Improve Core Web Vitals scores',
     status: 'NEW',
-    data: { cwvMetric: 'lcp', currentScore: 3200, targetScore: 2500 },
+    data: {
+      cwvMetric: 'lcp',
+      currentScore: 3200,
+      targetScore: 2500,
+      i18n: {
+        fr_fr: {
+          title: 'Corriger les problèmes CWV',
+          description: 'Améliorer les scores Core Web Vitals',
+        },
+      },
+    },
     runbook: 'https://wiki.example.com/runbooks/cwv-optimization',
     guidance: { steps: ['Review affected pages', 'Optimize LCP resources', 'Re-audit'] },
     tags: ['performance', 'cwv'],
diff --git a/test/it/postgres/seed-data/suggestions.js b/test/it/postgres/seed-data/suggestions.js
index 5e719d16ef..71e7d9e04d 100644
--- a/test/it/postgres/seed-data/suggestions.js
+++ b/test/it/postgres/seed-data/suggestions.js
@@ -27,7 +27,16 @@ export const suggestions = [
     type: 'CODE_CHANGE',
     rank: 1,
     status: 'NEW',
-    data: { title: 'Update hero image', from: '/old-hero.png', to: '/new-hero.webp' },
+    data: {
+      title: 'Update hero image',
+      from: '/old-hero.png',
+      to: '/new-hero.webp',
+      i18n: {
+        fr_fr: {
+          title: "Mettre à jour l'image principale",
+        },
+      },
+    },
     kpi_deltas: { estimatedKPILift: 0.15 },
   },
   {
diff --git a/test/it/shared/tests/opportunities.js b/test/it/shared/tests/opportunities.js
index 9ce91f1a99..094d5efac6 100644
--- a/test/it/shared/tests/opportunities.js
+++ b/test/it/shared/tests/opportunities.js
@@ -79,6 +79,36 @@ export default function opportunityTests(getHttpClient, resetData) {
         const res = await http.admin.get('/sites/not-a-uuid/opportunities');
         expect(res.status).to.equal(400);
       });
+
+      it('user: returns French title and description when locale=fr_fr', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`/sites/${SITE_1_ID}/opportunities?locale=fr_fr`);
+        expect(res.status).to.equal(200);
+        expect(res.body).to.be.an('array').with.lengthOf(2);
+
+        const oppty1 = res.body.find((o) => o.id === OPPTY_1_ID);
+        expect(oppty1).to.exist;
+        expect(oppty1.title).to.equal('Corriger les problèmes CWV');
+        expect(oppty1.description).to.equal('Améliorer les scores Core Web Vitals');
+        expect(oppty1.data).to.not.have.property('i18n');
+      });
+
+      it('user: returns English when locale is omitted', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`/sites/${SITE_1_ID}/opportunities`);
+        expect(res.status).to.equal(200);
+
+        const oppty1 = res.body.find((o) => o.id === OPPTY_1_ID);
+        expect(oppty1.title).to.equal('Fix CWV issues');
+        expect(oppty1.description).to.equal('Improve Core Web Vitals scores');
+      });
+
+      it('user: returns 400 for invalid locale format', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`/sites/${SITE_1_ID}/opportunities?locale=fr-FR`);
+        expect(res.status).to.equal(400);
+        expect(res.body).to.have.property('message', 'Invalid locale format');
+      });
     });
 
     describe('GET /sites/:siteId/opportunities/by-status/:status', () => {
@@ -124,6 +154,26 @@ export default function opportunityTests(getHttpClient, resetData) {
         expect(res.body[0].id).to.equal(OPPTY_1_ID);
         expect(res.body[0].status).to.equal('NEW');
       });
+
+      it('user: returns French title when locale=fr_fr', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(
+          `/sites/${SITE_1_ID}/opportunities/by-status/NEW?locale=fr_fr`,
+        );
+        expect(res.status).to.equal(200);
+        expect(res.body).to.be.an('array').with.lengthOf(1);
+        expect(res.body[0].title).to.equal('Corriger les problèmes CWV');
+        expect(res.body[0].description).to.equal('Améliorer les scores Core Web Vitals');
+      });
+
+      it('user: returns 400 for invalid locale format', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(
+          `/sites/${SITE_1_ID}/opportunities/by-status/NEW?locale=invalid`,
+        );
+        expect(res.status).to.equal(400);
+        expect(res.body).to.have.property('message', 'Invalid locale format');
+      });
     });
 
     describe('GET /sites/:siteId/opportunities/:opportunityId', () => {
@@ -168,6 +218,27 @@ export default function opportunityTests(getHttpClient, resetData) {
         const res = await http.admin.get(`/sites/${SITE_1_ID}/opportunities/not-a-uuid`);
         expect(res.status).to.equal(400);
       });
+
+      it('user: returns French title and description when locale=fr_fr', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(
+          `/sites/${SITE_1_ID}/opportunities/${OPPTY_1_ID}?locale=fr_fr`,
+        );
+        expect(res.status).to.equal(200);
+        expectOpportunityDto(res.body);
+        expect(res.body.title).to.equal('Corriger les problèmes CWV');
+        expect(res.body.description).to.equal('Améliorer les scores Core Web Vitals');
+        expect(res.body.data).to.not.have.property('i18n');
+      });
+
+      it('user: returns 400 for invalid locale format', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(
+          `/sites/${SITE_1_ID}/opportunities/${OPPTY_1_ID}?locale=FR_fr`,
+        );
+        expect(res.status).to.equal(400);
+        expect(res.body).to.have.property('message', 'Invalid locale format');
+      });
     });
 
     // ── Write endpoints ──
diff --git a/test/it/shared/tests/suggestions.js b/test/it/shared/tests/suggestions.js
index 108b20fc9a..0724fd438c 100644
--- a/test/it/shared/tests/suggestions.js
+++ b/test/it/shared/tests/suggestions.js
@@ -79,6 +79,34 @@ export default function suggestionTests(getHttpClient, resetData) {
         expect(res.status).to.equal(200);
         expect(res.body).to.be.an('array').with.lengthOf(0);
       });
+
+      it('user: returns French title in data when locale=fr_fr', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`${BASE}?locale=fr_fr`);
+        expect(res.status).to.equal(200);
+        expect(res.body).to.be.an('array').with.lengthOf(3);
+
+        const sugg1 = res.body.find((s) => s.id === SUGG_1_ID);
+        expect(sugg1).to.exist;
+        expect(sugg1.data.title).to.equal("Mettre à jour l'image principale");
+        expect(sugg1.data).to.not.have.property('i18n');
+      });
+
+      it('user: returns English title when locale is omitted', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(BASE);
+        expect(res.status).to.equal(200);
+
+        const sugg1 = res.body.find((s) => s.id === SUGG_1_ID);
+        expect(sugg1.data.title).to.equal('Update hero image');
+      });
+
+      it('user: returns 400 for invalid locale format', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`${BASE}?locale=fr`);
+        expect(res.status).to.equal(400);
+        expect(res.body).to.have.property('message', 'Invalid locale format');
+      });
     });
 
     describe('GET .../suggestions/paged/:limit', () => {
@@ -214,6 +242,22 @@ export default function suggestionTests(getHttpClient, resetData) {
         const res = await http.admin.get(`${BASE}/not-a-uuid`);
         expect(res.status).to.equal(400);
       });
+
+      it('user: returns French title in data when locale=fr_fr', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`${BASE}/${SUGG_1_ID}?locale=fr_fr`);
+        expect(res.status).to.equal(200);
+        expectSuggestionDto(res.body);
+        expect(res.body.data.title).to.equal("Mettre à jour l'image principale");
+        expect(res.body.data).to.not.have.property('i18n');
+      });
+
+      it('user: returns 400 for invalid locale format', async () => {
+        const http = getHttpClient();
+        const res = await http.user.get(`${BASE}/${SUGG_1_ID}?locale=fr-fr`);
+        expect(res.status).to.equal(400);
+        expect(res.body).to.have.property('message', 'Invalid locale format');
+      });
     });
 
     describe('GET .../suggestions/:suggestionId/fixes', () => {
diff --git a/test/utils/validations.test.js b/test/utils/validations.test.js
index ba3a0fe7cb..26b1d5dff8 100644
--- a/test/utils/validations.test.js
+++ b/test/utils/validations.test.js
@@ -11,7 +11,7 @@
  */
 
 import { expect } from 'chai';
-import { validateRepoUrl, checkBodySize } from '../../src/utils/validations.js';
+import { validateRepoUrl, checkBodySize, isValidLocale } from '../../src/utils/validations.js';
 
 // Helper to build Uint8Array of given length
 function makeBytes(len) {
@@ -58,4 +58,28 @@ describe('utils/validations', () => {
       expect(checkBodySize(undefined, 1)).to.be.true;
     });
   });
+
+  describe('isValidLocale', () => {
+    it('returns true for undefined or null', () => {
+      expect(isValidLocale(undefined)).to.be.true;
+      expect(isValidLocale(null)).to.be.true;
+    });
+
+    it('returns true for valid locale format', () => {
+      expect(isValidLocale('fr_fr')).to.be.true;
+      expect(isValidLocale('ja_jp')).to.be.true;
+      expect(isValidLocale('en_us')).to.be.true;
+    });
+
+    it('returns false for invalid locale format', () => {
+      expect(isValidLocale('fr')).to.be.false;
+      expect(isValidLocale('FR_FR')).to.be.false;
+      expect(isValidLocale('fr-fr')).to.be.false;
+      expect(isValidLocale('fr_')).to.be.false;
+      expect(isValidLocale('_fr')).to.be.false;
+      expect(isValidLocale('')).to.be.false;
+      expect(isValidLocale(123)).to.be.false;
+      expect(isValidLocale({})).to.be.false;
+    });
+  });
 });