vinext

On a server, keeping the base locale unprefixed — /about beside /zh/about — is usually a proxy that rewrites /about onto /en/about. On vinext that rewrite has a cost you do not see in the browser: vinext treats a rewritten request as resolved rather than requested, and only maps requested RSC navigations onto the shared cache key. Every client navigation in the base locale carries the router's state fingerprint, is never normalized, and answers Cache-Control: no-store. On Cloudflare that is a BYPASS on every page change in the base locale, while /zh/* hits the cache.

@best-i18n/vinext-unprefixed-locale removes the rewrite instead of working around it. It mirrors app/[locale] into a route group whose files import the originals and pin the locale, so /about matches a route directly. It is the same mirror as the static export package, run from a Vite plugin and meant for a server.

app/
  [locale]/          what you write
    layout.tsx
    blog/[...slug]/page.tsx
  (unprefixed)/      what is generated, gitignored
    layout.tsx       → imports [locale]/layout, params.locale pinned to 'en'
    blog/[...slug]/page.tsx

Setup

pnpm add @best-i18n/vinext-unprefixed-locale

// vite.config.ts
import { unprefixedLocale } from '@best-i18n/vinext-unprefixed-locale'
import { i18n } from 'best-i18n/vite'
import vinext from 'vinext'
import { defineConfig } from 'vite'
import { i18nConfig } from './src/i18n/config'

export default defineConfig({
  plugins: [
    unprefixedLocale({
      defaultLocale: i18nConfig.baseLocale,
      localeParam: i18nConfig.localeParam,
    }),
    i18n({ ...i18nConfig, messagesDir }),
    vinext(),
  ],
})

The plugin writes the mirror when Vite resolves its config, before vinext scans the app directory, and regenerates it while vite dev runs whenever a file under [locale] is added, removed or changed. The same i18nConfig feeds the compiler and the mirror, so the locales are described once.

Then take the rewrite out of the proxy. If the proxy did nothing else, delete it.

What changes on a server

A static export only has the files it built. A server still has [locale] at the root, which matches more than the locales:

/en/... still renders. Redirect it to the one canonical URL, in next.config.ts rather than a proxy:

// next.config.ts
async redirects() {
  return [
    { source: '/en', destination: '/', permanent: true },
    { source: '/en/:path*', destination: '/:path*', permanent: true },
  ]
}

Any unknown single-segment path reaches [locale] as a locale. Before, the proxy turned /foo into /en/foo, a 404. Now /foo is [locale] with locale: 'foo', and whatever the layout does with it decides between a 404 and a 500. Check it in the layout:

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

function assertLocale(locale: string): asserts locale is Locale {
  if (!i18nConfig.locales.includes(locale)) notFound()
}

export async function generateMetadata({ params }) {
  const { locale } = await params
  assertLocale(locale)
  // …
}

export default async function Layout({ children, params }) {
  const { locale } = await params
  assertLocale(locale)
  // …
}

Not dynamicParams = false: it cascades to every segment below, and a page like /prompts/[id] would 404 for anything published after the build.

Reading the locale on the server. If the app reads it from the [locale] root param, as best-i18n's vinext setup does with getCurrentRootParams(), the mirror has no such segment and the read comes back empty. Fall back to the base locale, which is the right answer for every mirrored route:

// src/i18n/server.ts
export function getLocale(): Locale {
  return localeFromRender() ?? i18nConfig.baseLocale
}

Options

generate(options) and a CLI are exported for running it outside Vite:

pnpm exec vinext-unprefixed-locale --locale en          # once
pnpm exec vinext-unprefixed-locale --locale en --watch  # keep going

The generated files, the route segment config repeated as literals and the limits — no dynamic segment directly under [locale], two root layouts so a locale switch is a full page load, export * hiding exports — are the same as for the static export.