i18n by next-intl

frontend/src/i18n.ts

@@ -0,0 +1,12 @@
+import { notFound } from "next/navigation";
+import { getRequestConfig } from "next-intl/server";
+
+const locales = ["en", "ja"];
+
+export default getRequestConfig(async ({ locale }) => {
+  if (!locales.includes(locale as any)) notFound();
+
+  return {
+    messages: (await import(`../messages/${locale}.json`)).default,
+  };
+});