feat(i18n): add locale-based routing setup

Add next-intl routing config, proxy middleware, and update request config to use requestLocale from middleware. Add @/i18n/* path alias to tsconfig.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/i18n/request.ts

@@ -1,14 +1,12 @@
-import { getRequestConfig } from "next-intl/server";
-import { headers } from "next/headers";
+import { getRequestConfig } from 'next-intl/server';
+import { hasLocale } from 'next-intl';
+import { routing } from './routing';
 
-export default getRequestConfig(async () => {
-  const headersList = await headers();
-  const acceptLanguage = headersList.get("accept-language");
-
-  const browserLocale = acceptLanguage?.split(",")[0]?.split("-")[0];
-
-  const supportedLocales = ["en", "pl"];
-  const locale = browserLocale && supportedLocales.includes(browserLocale) ? browserLocale : "en";
+export default getRequestConfig(async ({ requestLocale }) => {
+  const requested = await requestLocale;
+  const locale = hasLocale(routing.locales, requested)
+    ? requested
+    : routing.defaultLocale;
 
   return {
     locale,

src/i18n/routing.ts

@@ -0,0 +1,7 @@
+import { defineRouting } from 'next-intl/routing';
+
+export const routing = defineRouting({
+  locales: ['en', 'pl'],
+  defaultLocale: 'en',
+  localePrefix: 'as-needed',
+});

src/proxy.ts

@@ -0,0 +1,10 @@
+import createMiddleware from 'next-intl/middleware';
+import { routing } from './i18n/routing';
+
+export default createMiddleware(routing);
+
+export const config = {
+  matcher: [
+    '/((?!api|_next|_vercel|.*\\..*).*)',
+  ],
+};

tsconfig.json

@@ -24,6 +24,7 @@
       "@/lib/*": ["./src/lib/*"],
       "@/hooks/*": ["./src/hooks/*"],
       "@/app/*": ["./src/app/*"],
+      "@/i18n/*": ["./src/i18n/*"],
       "@/constants": ["./src/constants.ts"]
     }
   },