Next.js

Internationalized Routing in the App Router

28 min Lesson 70 of 80

Internationalized Routing in the App Router

This lesson expands the Next.js path with an advanced topic from the official Next.js documentation. The goal is not only to memorize an option or file name, but to understand its impact on rendering, caching, security, and deployment.

After this lesson you should be able to apply the topic in a real project, choose the right boundary for it, and explain it as a reviewable engineering decision.

Core Concepts

[lang] segments
locale validation
localized metadata
dictionary loading
language redirects

Practical Example

// app/[lang]/layout.tsx
import { notFound } from 'next/navigation'

const locales = ['en', 'ar'] as const

export default async function LocaleLayout({ children, params }: LayoutProps<'/[lang]'>) {
  const { lang } = await params
  if (!locales.includes(lang as any)) notFound()
  return <html lang={lang} dir={lang === 'ar' ? 'rtl' : 'ltr'}><body>{children}</body></html>
}

This lesson is aligned with these official Next.js documentation areas: Internationalization and routing docs.

Why It Matters

In production applications, this topic affects page speed, data freshness, authorization clarity, and operational reliability after deployment.

Implementation Workflow

Decide whether the data is public or user-specific.
Choose the smallest part of the tree that needs this behavior.
Connect the example to a real route and add a small verification check.
Document the effect on caching and deployment.

Hands-on Practice

Create English and Arabic dictionaries loaded from a locale-aware layout.

Localized routing can duplicate canonical URLs if metadata and alternates are not planned carefully.

Summary

Judge the implementation by how clear the decision is, whether the behavior is correct after build, and how easily it can be traced in production.