i18n by next-intl

frontend/src/middleware.ts

@@ -0,0 +1,12 @@
+import createMiddleware from "next-intl/middleware";
+import { locales, localePrefix } from "./navigation";
+
+export default createMiddleware({
+  defaultLocale: "en",
+  localePrefix,
+  locales,
+});
+
+export const config = {
+  matcher: ["/", "/(ja|en)/:path*"],
+};