feat(front-end): ssr i18n fix

frontend/src/app/app.config.ts

@@ -1,17 +1,25 @@
 import {
   ApplicationConfig,
+  provideAppInitializer,
   provideZoneChangeDetection,
   importProvidersFrom,
+  inject,
+  REQUEST,
 } from '@angular/core';
 import {
   provideRouter,
   withComponentInputBinding,
   withInMemoryScrolling,
   withViewTransitions,
+  Router,
 } from '@angular/router';
 import { routes } from './app.routes';
 import { provideHttpClient, withInterceptors } from '@angular/common/http';
-import { TranslateModule, TranslateLoader } from '@ngx-translate/core';
+import {
+  TranslateLoader,
+  TranslateModule,
+  TranslateService,
+} from '@ngx-translate/core';
 import {
   provideTranslateHttpLoader,
   TranslateHttpLoader,
@@ -22,6 +30,22 @@ import {
   withEventReplay,
 } from '@angular/platform-browser';
 import { serverOriginInterceptor } from './core/interceptors/server-origin.interceptor';
+import { catchError, firstValueFrom, of } from 'rxjs';
+
+type SupportedLang = 'it' | 'en' | 'de' | 'fr';
+const SUPPORTED_LANGS: readonly SupportedLang[] = ['it', 'en', 'de', 'fr'];
+
+function resolveLangFromUrl(url: string): SupportedLang {
+  const firstSegment = (url || '/')
+    .split('?')[0]
+    .split('#')[0]
+    .split('/')
+    .filter(Boolean)[0]
+    ?.toLowerCase();
+  return SUPPORTED_LANGS.includes(firstSegment as SupportedLang)
+    ? (firstSegment as SupportedLang)
+    : 'it';
+}
 
 export const appConfig: ApplicationConfig = {
   providers: [
@@ -50,6 +74,32 @@ export const appConfig: ApplicationConfig = {
         },
       }),
     ),
+    provideAppInitializer(() => {
+      const translate = inject(TranslateService);
+      const router = inject(Router);
+      const request = inject(REQUEST, { optional: true }) as
+        | { url?: string }
+        | null;
+
+      translate.addLangs([...SUPPORTED_LANGS]);
+      translate.setDefaultLang('it');
+      const requestedUrl =
+        (typeof request?.url === 'string' && request.url) || router.url || '/';
+      const lang = resolveLangFromUrl(requestedUrl);
+
+      return firstValueFrom(
+        translate.use(lang).pipe(
+          catchError((error) => {
+            console.error('[i18n] Failed to preload language for SSR', {
+              lang,
+              requestedUrl,
+              error,
+            });
+            return of({});
+          }),
+        ),
+      ).then(() => undefined);
+    }),
     provideClientHydration(withEventReplay()),
   ],
 };