Next.js i18n: Why Library Choice Matters More Than You Think

The key insight: Your internationalization library choice in Next.js isn't just about syntax—it fundamentally shapes your app's architecture, performance characteristics, and long-term maintainability, especially with App Router and React Server Components.

After diving deep into LogRocket's comprehensive Next.js i18n guide, what struck me wasn't the usual "how to translate strings" tutorial. Instead, it revealed how modern Next.js features like App Router and RSC create new architectural constraints that make library choice critical.

The App Router Reality Check

With traditional Pages Router, i18n was mostly a client-side concern. App Router changes everything—and Next.js 16 takes it further with async params and the new proxy.ts file (replacing middleware.ts). Your translations now need to work seamlessly across server components, client components, and the boundary between them.

1// App Router structure for Next.js 16+
2app/
3  [locale]/
4    layout.tsx    // Server component - params are now async!
5    page.tsx      // Server component
6    components/
7      ClientForm.tsx // Client component needs locale too
8

The guide demonstrates how next-intl handles this elegantly with its NextIntlClientProvider, while Lingui requires more manual orchestration. This isn't just developer convenience—it affects bundle size and hydration complexity.

Performance Implications You Haven't Considered

Here's where it gets interesting: Server Components can render translations on the server, reducing client bundle size. But only if your i18n setup supports it properly.

next-intl shines here because it's designed for Next.js's hybrid rendering model:

1// Server Component - translations bundled server-side
2import {getTranslations} from 'next-intl/server';
3
4export default async function ServerPage({
5  params
6}: {
7  params: Promise<{locale: string}>;
8}) {

With Lingui, you need more manual configuration to achieve similar bundle splitting, and the deprecation of their Babel/SWC plugins adds migration overhead.

The Proxy Strategy That Changes Everything

The guide's proxy patterns (formerly middleware in Next.js 15 and earlier) solve a problem most tutorials ignore: selective internationalization. You don't always want everything internationalized.

1// proxy.ts (called middleware.ts before Next.js 16)
2import createMiddleware from 'next-intl/middleware';
3import {routing} from './i18n/routing';
4
5export default createMiddleware(routing);
6
7export const config = {
8  // Match all pathnames except API, static assets, and files with dots
9  matcher: '/((?!api|trpc|_next|_vercel|.*\\..*).*)'
10};

This matcher configuration in proxy.ts is crucial for real-world apps. Your admin dashboard, API endpoints, and static assets don't need locale detection—and including them creates unnecessary complexity and potential bugs.

Developer Experience That Scales

What the guide reveals about next-intl's automatic message extraction is game-changing for team workflows:

1# During development, messages automatically extracted
2npm run dev
3# Generates/updates messages/en.json, messages/es.json

Compare this to manually maintaining message files or complex build-time extraction scripts. For teams managing hundreds of translation keys across multiple features, this automation prevents the message file drift that kills i18n projects.

Lingui requires more setup post-SWC transition, though it's still viable if you're already invested in its ecosystem.

The Locale Detection Nuances

The guide covers three detection strategies, but doesn't emphasize which matters most: cookie persistence.

1// Proxy detection priority (Next.js 16+)
21. URL path (/es/dashboard) - explicit user choice
32. Cookie value - returning user preference  
43. Accept-Language header - browser default
54. Default locale - fallback

This hierarchy respects user intent while providing sensible defaults. Too many implementations rely solely on headers, creating frustrating experiences where users can't maintain language preferences.

Real-World Gotchas

The tutorial touches on pseudo-locales for QA, but doesn't stress how critical this is for layout testing:

1{
2  "welcome": "[Welcome to our app]",
3  "longMessage": "[This is an intentionally very long message to test layout overflow in your components]"
4}

German translations often 30-50% longer than English. Spanish can be shorter but uses more vertical space with accents. Pseudo-locales catch these issues before your German users see broken layouts.

Architecture Decisions That Compound

What the guide illustrates—though doesn't explicitly state—is how early i18n choices cascade through your entire application:

• Route structure: /[locale]/dashboard vs domain-based routing affects SEO strategy
• Bundle strategy: Server-side translations vs client hydration impacts Core Web Vitals
• Type safety: Auto-generated types from message keys vs runtime string errors
• Team workflow: Automatic extraction vs manual message file maintenance

next-intl makes better default choices for Next.js-first applications, while Lingui offers more flexibility at the cost of configuration complexity.

Why This Matters

Internationalization isn't just a feature—it's an architectural decision that touches routing, bundling, server/client boundaries, and team workflows. The App Router era makes these choices more consequential, not less.

Choose next-intl if you want opinionated defaults that work well with Next.js patterns. Choose Lingui if you need its specific features and don't mind the additional configuration overhead.

But choose deliberately, early, and with your team's long-term maintenance capacity in mind. The "simple" i18n setup you skip planning for becomes the technical debt that complicates every feature for years.

Next steps: Audit your current i18n setup against App Router patterns, migrate middleware.ts to proxy.ts if you're on Next.js 16+, implement pseudo-locales in development, and test your proxy matcher configuration with realistic traffic patterns. Don't forget to update your params to use async/await—it's now required. The investment in proper i18n architecture pays dividends in user reach and developer velocity.