fix i18n runtime scoping for SSR requests

Create a dedicated i18next instance per SSR request and remove server context-storage coupling from translation runtime, while keeping a separate client singleton path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/i18n/index.ts

@@ -1,6 +1,6 @@
 import type { i18n as I18nInstance } from 'i18next';
 
-import { getActiveI18nInstance } from '@/lib/translation';
+import { getClientI18nInstance } from '@/lib/translation/client';
 
 import { defaultLocale, supportedLocales, type SupportedLocale } from './constants';
 
@@ -15,5 +15,5 @@ export const normalizeLocale = (locale?: string): SupportedLocale => {
 };
 
 export const getActiveI18n = (): I18nInstance | undefined => {
-  return getActiveI18nInstance();
+  return import.meta.env.SSR ? undefined : getClientI18nInstance();
 };

src/lib/translation/client.ts

@@ -0,0 +1,15 @@
+import type { i18n as I18nInstance } from 'i18next';
+
+import { createI18nInstance, initI18nInstance } from '@/lib/translation';
+
+let clientI18n: I18nInstance | undefined;
+
+export const createI18nForClient = async (language?: string) => {
+  if (!clientI18n) {
+    clientI18n = createI18nInstance(false);
+  }
+
+  return initI18nInstance(clientI18n, language, false);
+};
+
+export const getClientI18nInstance = () => clientI18n;

src/lib/translation/index.ts

@@ -1,14 +1,11 @@
 import i18next, { type i18n as I18nInstance } from 'i18next';
 import LanguageDetector from 'i18next-browser-languagedetector';
 import I18NextHttpBackend from 'i18next-http-backend';
-import { tryGetContext } from 'hono/context-storage';
 
 import { defaultLocale, localeCookieKey, supportedLocales, type SupportedLocale } from '@/i18n/constants';
 
 const runtimeNamespace = 'translation';
 
-let clientI18n: I18nInstance | undefined;
-
 const normalizeLanguage = (language?: string): SupportedLocale => {
   if (!language) return defaultLocale;
   const normalized = language.toLowerCase().split('-')[0] as SupportedLocale;
@@ -23,18 +20,22 @@ const getLoadPath = () => {
   return '/locales/{{lng}}/{{lng}}.json';
 };
 
-const createInstance = () => {
+export const createI18nInstance = (forServer: boolean) => {
   const instance = i18next.createInstance();
 
   instance.use(I18NextHttpBackend);
-  if (!import.meta.env.SSR) {
+  if (!forServer) {
     instance.use(LanguageDetector);
   }
 
   return instance;
 };
 
-const initInstance = async (instance: I18nInstance, language?: string) => {
+export const initI18nInstance = async (
+  instance: I18nInstance,
+  language?: string,
+  forServer: boolean = import.meta.env.SSR,
+) => {
   const lng = normalizeLanguage(language);
 
   if (!instance.isInitialized) {
@@ -52,7 +53,7 @@ const initInstance = async (instance: I18nInstance, language?: string) => {
       backend: {
         loadPath: getLoadPath(),
       },
-      ...(import.meta.env.SSR
+      ...(forServer
         ? {}
         : {
             detection: {
@@ -72,27 +73,3 @@ const initInstance = async (instance: I18nInstance, language?: string) => {
 
   return instance;
 };
-
-export const createI18nForRuntime = async (language?: string) => {
-  if (import.meta.env.SSR) {
-    const serverI18n = await initInstance(createInstance(), language);
-    const context = tryGetContext<any>();
-    context?.set?.('i18n', serverI18n);
-    return serverI18n;
-  }
-
-  if (!clientI18n) {
-    clientI18n = createInstance();
-  }
-
-  return initInstance(clientI18n, language);
-};
-
-export const getActiveI18nInstance = () => {
-  if (!import.meta.env.SSR) {
-    return clientI18n;
-  }
-
-  const context = tryGetContext<any>();
-  return context?.get?.('i18n') as I18nInstance | undefined;
-};

src/main.ts

@@ -5,8 +5,11 @@ import { createPinia } from 'pinia';
 import { createSSRApp } from 'vue';
 import { RouterView } from 'vue-router';
 
+import type { i18n as I18nInstance } from 'i18next';
 import I18NextVue from 'i18next-vue';
-import { createI18nForRuntime } from '@/lib/translation';
+
+import { createI18nInstance, initI18nInstance } from '@/lib/translation';
+import { createI18nForClient } from '@/lib/translation/client';
 
 import { withErrorBoundary } from './lib/hoc/withErrorBoundary';
 import createAppRouter from './routes';
@@ -18,7 +21,7 @@ const getSerializedAppData = () => {
     return JSON.parse(document.getElementById('__APP_DATA__')?.innerText || '{}') as Record<string, any>;
 };
 
-export async function createApp(lng: string = 'en') {
+export async function createApp(lng: string = 'en', i18next?: I18nInstance) {
     const pinia = createPinia();
     const app = createSSRApp(withErrorBoundary(RouterView));
     
@@ -32,8 +35,13 @@ export async function createApp(lng: string = 'en') {
         }
     });
     app.use(pinia);
-    const i18next = await createI18nForRuntime(lng);
+    const runtimeI18n = import.meta.env.SSR
-    app.use(I18NextVue, { i18next });
+        ? (i18next ?? createI18nInstance(true))
+        : await createI18nForClient(lng);
+    if (import.meta.env.SSR) {
+        await initI18nInstance(runtimeI18n, lng, true);
+    }
+    app.use(I18NextVue, { i18next: runtimeI18n });
     app.use(PiniaColada, {
         pinia,
         plugins: [

src/server/routes/ssr.ts

@@ -3,6 +3,8 @@ import { renderSSRHead } from '@unhead/vue/server';
 import { streamText } from 'hono/streaming';
 import { renderToWebStream } from 'vue/server-renderer';
 
+import { localeCookieKey } from '@/i18n';
+import { createI18nInstance, initI18nInstance } from '@/lib/translation';
 import { buildBootstrapScript } from '@/lib/manifest';
 import { createApp } from '@/main';
 import { htmlEscape } from '@/server/utils/htmlEscape';
@@ -25,7 +27,10 @@ export function registerSSRRoutes(app: Hono) {
     const nonce = crypto.randomUUID();
     const url = new URL(c.req.url);
     const lang = c.get("language")
-    const { app: vueApp, router, head, pinia, bodyClass, queryCache } = await createApp(lang);
+    const localeFromCookie = parseCookie(c.req.header('cookie'), localeCookieKey);
+    const i18next = createI18nInstance(true);
+    await initI18nInstance(i18next, localeFromCookie ?? lang, true);
+    const { app: vueApp, router, head, pinia, bodyClass, queryCache } = await createApp(localeFromCookie ?? lang, i18next);
 
     vueApp.provide("honoContext", c);
 
@@ -44,7 +49,7 @@ export function registerSSRRoutes(app: Hono) {
       const appStream = renderToWebStream(vueApp, ctx);
 
       // HTML Head
-      await stream.write(`<!DOCTYPE html><html lang='${lang}'><head>`);
+      await stream.write(`<!DOCTYPE html><html lang='${i18next.resolvedLanguage ?? lang}'><head>`);
       await stream.write("<base href='" + url.origin + "'/>");
 
       // SSR Head tags
@@ -74,7 +79,7 @@ export function registerSSRRoutes(app: Hono) {
       Object.assign(ctx, {
         $p: pinia.state.value,
         $colada: serializeQueryCache(queryCache),
-        $locale: lang,
+        $locale: i18next.resolvedLanguage ?? lang,
       });
 
       // App data script