Dev

apps/api/api/index.ts

@@ -7,6 +7,7 @@ import express, { Express, Request, Response } from 'express';
 import morgan from 'morgan';
 import { stream as loggerStream } from './config/logger';
 import { metricsMiddleware } from './middleware/metrics.middleware';
+import { languageMiddleware } from './middleware/language.middleware';
 import metricsRouter from './routes/metrics.routes';
 import admin from 'firebase-admin';
 import cors from 'cors';
@@ -113,6 +114,10 @@ app.use(
 // Audit log for sensitive routes.
 app.use(auditLogger);
 
+// Resolve the user's UI language (query > body > Accept-Language) and expose it to
+// all downstream services so AI generation replies in the right language.
+app.use(languageMiddleware);
+
 app.use('/projects', projectRoutes);
 app.use('/project', brandingRoutes);
 app.use('/project', diagramRoutes);

apps/api/api/interfaces/express.interface.ts

@@ -3,6 +3,8 @@ import admin from 'firebase-admin';
 
 export interface CustomRequest extends Request {
   user?: admin.auth.DecodedIdToken;
+  /** Resolved UI language ('en' | 'fr'), set by languageMiddleware. */
+  language?: string;
   policyWarning?: {
     requiresFinalization: boolean;
     finalizeEndpoint: string;

apps/api/api/middleware/language.middleware.ts

@@ -0,0 +1,24 @@
+import { Request, Response, NextFunction } from 'express';
+import { normalizeLanguage, runWithLanguage } from '../utils/request-language';
+
+/**
+ * Resolve the user's UI language for the request and expose it two ways:
+ *  - `req.language` (typed on CustomRequest) for direct access in controllers;
+ *  - an AsyncLocalStorage context so PromptService (and any downstream service)
+ *    can read it without threading the value through every call.
+ *
+ * Resolution priority: `?lang=` query > `language` body field > Accept-Language
+ * header > default 'en'.
+ */
+export function languageMiddleware(req: Request, _res: Response, next: NextFunction): void {
+  const fromQuery = typeof req.query.lang === 'string' ? req.query.lang : undefined;
+  const fromBody =
+    req.body && typeof req.body.language === 'string' ? (req.body.language as string) : undefined;
+  const headerValue = req.headers['accept-language'];
+  const fromHeader = typeof headerValue === 'string' ? headerValue.split(',')[0] : undefined;
+
+  const language = normalizeLanguage(fromQuery || fromBody || fromHeader);
+  (req as Request & { language?: string }).language = language;
+
+  runWithLanguage(language, () => next());
+}

apps/api/api/services/BusinessPlan/businessPlan.service.ts

@@ -8,6 +8,7 @@ import { GenericService, IPromptStep, ISectionResult } from '../common/generic.s
 import { SectionModel } from '../../models/section.model';
 import { PdfService } from '../pdf.service';
 import { cacheService, CacheOptions } from '../cache.service';
+import { getRequestLanguage } from '../../utils/request-language';
 import crypto from 'crypto';
 import { AGENT_COVER_PROMPT } from './prompts/agent-cover.prompt';
 import { AGENT_COMPANY_SUMMARY_PROMPT } from './prompts/agent-company-summary.prompt';
@@ -89,7 +90,9 @@ export class BusinessPlanService extends GenericService {
     const typography = project.analysisResultModel?.branding?.typography || {
       primary: 'Arial, sans-serif',
     };
-    const language = 'fr';
+    // Use the user's request language instead of a hard-coded 'fr' so the plan is
+    // generated in the language selected in the UI (falls back to 'en').
+    const language = getRequestLanguage() === 'fr' ? 'French' : 'English';
 
     // Create brand context for all agents
     const brandContext = `Brand: ${brandName}\nLogo SVG: ${logoSvg}\nBrand Colors: ${JSON.stringify(

apps/api/api/services/prompt.service.ts

@@ -9,6 +9,7 @@ dotenv.config();
 
 import { LLMProvider, LLMOptions, AI_CONFIG } from '../config/ai.config';
 import { withGeminiFallback } from '../utils/gemini-fallback';
+import { getRequestLanguage } from '../utils/request-language';
 export { LLMProvider, LLMOptions };
 
 
@@ -24,6 +25,12 @@ export interface PromptConfig {
   userId?: string;
   promptType?: string;
   skipQuotaCheck?: boolean;
+  /**
+   * User UI language ('en' | 'fr'). When set, a language directive is injected so
+   * the model generates content in the requested language. Resolved from the
+   * request (query `lang` / body `language` / Accept-Language header) upstream.
+   */
+  language?: string;
 }
 
 export interface AIChatMessage {
@@ -44,6 +51,7 @@ export interface PromptRequest {
   userId?: string;
   promptType?: string;
   skipQuotaCheck?: boolean;
+  language?: string;
 }
 
 export interface AIResponse {
@@ -422,6 +430,27 @@ export class PromptService {
     }
   }
 
+  /**
+   * Build a strong directive that forces the model to answer in the user's language.
+   * Returns an empty string when no (or an unknown) language is provided, leaving
+   * existing behavior unchanged.
+   */
+  private buildLanguageDirective(language?: string): string {
+    if (!language) {
+      return '';
+    }
+    const normalized = language.toLowerCase();
+    const label = normalized.startsWith('fr')
+      ? 'French (Français)'
+      : normalized.startsWith('en')
+        ? 'English'
+        : null;
+    if (!label) {
+      return '';
+    }
+    return `RESPONSE LANGUAGE (CRITICAL): You MUST write ALL generated content — every section, title, sentence, label and value — in ${label}. Do not mix languages. This instruction overrides any language implied by the examples or prompts below.`;
+  }
+
   public async runPrompt(request: PromptConfig, messages: AIChatMessage[]): Promise<string> {
     logger.info(
       `Running prompt for provider: ${request.provider}, model: ${
@@ -436,6 +465,7 @@ export class PromptService {
       userId,
       promptType,
       skipQuotaCheck = false,
+      language,
     } = request;
 
     if (!messages || messages.length === 0) {
@@ -492,6 +522,25 @@ export class PromptService {
       logger.info('Applied prompt modifications');
     }
 
+    // Force the output language. This is the single choke point for every AI
+    // feature/provider, so one directive here guarantees generated content is in
+    // the user's language (prevents wrong-language output). An explicit
+    // config.language wins; otherwise fall back to the request-scoped language.
+    const effectiveLanguage = language ?? getRequestLanguage();
+    const languageDirective = this.buildLanguageDirective(effectiveLanguage);
+    if (languageDirective && modifiedMessages.length > 0) {
+      // Append to the LAST message rather than inserting a new system message:
+      // this keeps message roles/adjacency intact (Gemini rejects consecutive
+      // same-role turns) and benefits from recency for stronger adherence.
+      const lastIdx = modifiedMessages.length - 1;
+      const last = modifiedMessages[lastIdx];
+      modifiedMessages = [
+        ...modifiedMessages.slice(0, lastIdx),
+        { ...last, content: `${last.content}\n\n${languageDirective}` },
+      ];
+      logger.info(`Injected language directive (language=${effectiveLanguage}).`);
+    }
+
     try {
       let result: string;
       switch (provider) {

apps/api/api/utils/request-language.ts

@@ -0,0 +1,32 @@
+import { AsyncLocalStorage } from 'async_hooks';
+
+export type SupportedLanguage = 'en' | 'fr';
+
+interface LanguageStore {
+  language: SupportedLanguage;
+}
+
+/**
+ * Request-scoped language store. The language middleware seeds this per request so
+ * that any service (notably PromptService) can read the user's language without it
+ * being threaded through every function signature.
+ */
+const storage = new AsyncLocalStorage<LanguageStore>();
+
+export function runWithLanguage<T>(language: SupportedLanguage, fn: () => T): T {
+  return storage.run({ language }, fn);
+}
+
+/** Current request's language, or undefined outside a request context. */
+export function getRequestLanguage(): SupportedLanguage | undefined {
+  return storage.getStore()?.language;
+}
+
+/** Normalize an arbitrary language hint to a supported language (defaults to 'en'). */
+export function normalizeLanguage(value: unknown): SupportedLanguage {
+  return String(value ?? '')
+    .toLowerCase()
+    .startsWith('fr')
+    ? 'fr'
+    : 'en';
+}

apps/appgen/apps/we-dev-client/src/api/appInfo.ts

@@ -1,21 +1,9 @@
+import { resolveInitialLocale } from "../utils/localeCookie";
+
 export const authService = {
   async appInfo() {
-    let language = "en";
-    try {
-      const settingsConfig = JSON.parse(
-        localStorage.getItem("settingsConfig") || "{}"
-      );
-      if (settingsConfig.language) {
-        language = settingsConfig.language;
-      } else {
-        // Get browser language setting
-        const browserLang = navigator.language.toLowerCase();
-        // Set to Chinese if browser language is Chinese, otherwise English
-        language = browserLang.startsWith("zh") ? "zh" : "en";
-      }
-    } catch (error) {
-      console.log(error);
-    }
+    // Shared cross-app cookie is the source of truth; falls back to browser lang.
+    const language = resolveInitialLocale();
 
     const res = await fetch(
       `${process.env.REACT_APP_BASE_URL}/api/appInfo?language=${language}`,

apps/appgen/apps/we-dev-client/src/components/AiChat/chat/index.tsx

@@ -186,7 +186,7 @@ export const BaseChat = ({ uuid: propUuid }: { uuid?: string }) => {
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const messagesEndRef = useRef<HTMLDivElement>(null);
   const { otherConfig } = useChatStore();
-  const { t } = useTranslation();
+  const { t, i18n } = useTranslation();
   const [checkCount, setCheckCount] = useState(0);
   const [visible, setVisible] = useState(false);
   const [baseModal, setBaseModal] = useState<IModelOption>({
@@ -493,6 +493,9 @@ export const BaseChat = ({ uuid: propUuid }: { uuid?: string }) => {
     body: {
       model: baseModal.value,
       mode: mode,
+      // User UI language so the AI answers/generates content in the right language.
+      // (Distinct from otherConfig.backendLanguage, which is the target programming language.)
+      language: i18n.language,
       otherConfig: {
         ...otherConfig,
         extra: {

apps/appgen/apps/we-dev-client/src/components/Settings/GeneralSettings.tsx

@@ -614,7 +614,7 @@ export function GeneralSettings() {
                   onChange={(value) => handleLanguageChange(value)}
                   options={[
                     { value: "en", label: "English" },
-                    { value: "zh", label: "中文" },
+                    { value: "fr", label: "Français" },
                   ]}
                 />
               </div>
@@ -643,7 +643,7 @@ export function GeneralSettings() {
             onChange={(value) => handleLanguageChange(value)}
             options={[
               { value: "en", label: "English" },
-              { value: "zh", label: "中文" },
+              { value: "fr", label: "Français" },
             ]}
           />
         </div>

apps/appgen/apps/we-dev-client/src/hooks/useInit.ts

@@ -1,6 +1,7 @@
 import useThemeStore from '@/stores/themeSlice';
 import useUserStore from '@/stores/userSlice';
 import i18n from '@/utils/i18';
+import { readLocaleCookie } from '@/utils/localeCookie';
 import { useEffect } from 'react';
 import useMCPStore from '@/stores/useMCPSlice';
 import { eventEmitter } from '@/components/AiChat/utils/EventEmitter';
@@ -90,17 +91,18 @@ const useInit = (): { isDarkMode: boolean } => {
     // Version web - pas d'accès au système de fichiers local
     console.log('Local filesystem not available in web mode');
 
+    // Language priority: shared cross-app cookie > legacy settingsConfig > browser.
+    // The shared `idem_lang` cookie is the source of truth across all Idem apps.
     const settingsConfig = JSON.parse(localStorage.getItem('settingsConfig') || '{}');
-    if (settingsConfig.language) {
+    const cookieLang = readLocaleCookie();
+    if (cookieLang) {
+      i18n.changeLanguage(cookieLang);
+    } else if (settingsConfig.language === 'en' || settingsConfig.language === 'fr') {
       i18n.changeLanguage(settingsConfig.language);
     } else {
-      // Get browser language settings
       const browserLang = navigator.language.toLowerCase();
-      // If Chinese environment (including simplified and traditional), set to Chinese, otherwise set to English
-      const defaultLang = browserLang.startsWith('zh') ? 'zh' : 'en';
-
+      const defaultLang = browserLang.startsWith('fr') ? 'fr' : 'en';
       i18n.changeLanguage(defaultLang);
-      // Save to local settings
     }
 
     // Version web - pas de gestion de proxy système