version: "1.0.1" name: enable-i18n description: > Enable next-intl-based i18n in the shop template — locale-prefixed URLs, per-locale message catalogs, and a locale switcher. Use when the user wants "locale URLs", "multi-language", or "i18n" without Shopify Markets integration. For full Shopify Markets multi-region commerce (region-aware pricing, inventory, payments), use enable-shopify-markets instead — this skill is the routing/i18n layer only.

Enable i18n (next-intl, no Markets)

Wire next-intl into the template so the storefront serves locale-prefixed URLs (/en-US/products/foo), loads per-locale message catalogs, and exposes a locale switcher. The template ships single-locale by default with clean URLs (/products/foo) — this skill restores the i18n machinery.

Use `enable-shopify-markets` instead if you want region-aware pricing/inventory/payments. That skill builds on the same routing layer plus Markets-specific operations. If you only want URL prefixing and translated copy, this skill is the right one.

Source of truth: lib/i18n/index.ts

The locale list lives in lib/i18n/index.ts as locales and enabledLocales. Always read those at the start of the skill — don't hardcode a list. Adding new locales means editing that file plus the localeCurrency map; everything downstream (routing, sitemap, alternates, switcher) reads from it.

// lib/i18n/index.ts
export const locales = ["en-US", "en-GB", "de-DE", "fr-FR"] as const;
export const defaultLocale: Locale = "en-US";
export const enabledLocales: readonly Locale[] = locales;

What this skill turns on

1. lib/i18n/routing.ts and lib/i18n/navigation.ts (next-intl)
2. Route segment app/[locale]/ containing every page
3. proxy.ts middleware running next-intl/middleware
4. lib/params.ts getLocale() reading from next/root-params
5. lib/i18n/request.ts loading messages by resolved locale
6. Locale-prefixed canonicals + hreflang alternates in lib/seo.ts
7. Sitemap entries per locale
8. next.config.ts rewrites/redirects on /:locale/* sources
9. app/(unlocalized)/page.tsx fallback redirect to default locale
10. generateStaticParams on the root layout
11. (If enable-shopify-menus already ran) Re-enable LocaleCurrencySelector in the megamenu

Cache Components compatibility — read this first

The template runs with cacheComponents: true (Next.js 16). That changes a few things this skill needs to handle correctly. Skipping any of these will produce build errors that look unrelated:

A. There must be no app/layout.tsx above app/[locale]/

For [locale] to be recognized as a root param, the dynamic segment must be the root layout. After Step 2, the file at app/layout.tsx should be gone (moved into app/[locale]/layout.tsx). If both exist, rootParams.locale() returns undefined.

B. setRequestLocale is not used

next-intl docs sometimes show setRequestLocale(locale) calls in layouts/pages. Don't add them under cacheComponents. That helper writes to a request-scoped store and forces dynamic rendering — it defeats the cache. The rootParams + request-config pattern below makes it unnecessary because the resolved locale is already a cache key.

C. Don't swap next/link to next-intl's <Link>

The straightforward instinct is to replace every import Link from "next/link" with import { Link } from "@/lib/i18n/navigation". Don't. next-intl's Link reads request context (locale) on render; in a server-component tree under cacheComponents, that triggers:

Error: Route "/[locale]/..." accessed [...] which is not defined in the `samples` of `unstable_instant`.

or a generic "blocking route" prerender failure.

Do this instead: keep next/link and let proxy.ts middleware redirect unprefixed paths (/products/foo → /en-US/products/foo). Internal links work; there's a one-time middleware redirect on click for unprefixed hrefs. Trade a few redirects for a clean prerender.

If you must locale-prefix a programmatic URL (server actions, redirect(), permanentRedirect()), build the path yourself: ` /${await getLocale()}/account/login `.

D. unstable_instant samples need locale in params

Any route that exports unstable_instant (currently: products [handle], collections [handle], search) needs locale added to every sample, or the build fails:

Error: Route "/[locale]/products/[handle]" accessed root param "locale"
       which is not defined in the `samples` of `unstable_instant`.

Fix:

export const unstable_instant = {
  samples: [
    {
      params: { locale: "en-US", handle: "__placeholder__" }, // ← add locale
      searchParams: { variant: "1" },
      cookies: [{ name: "shopify_cartId", value: null }],
    },
  ],
};

E. unstable_instant samples need headers declarations if any layout-level server component reads headers()

This is easy to forget. If you (or a downstream skill) adds a server component to the layout that calls headers() — e.g. a "Shipping to {postal}" bar reading x-vercel-ip-postal-code — every unstable_instant sample in the app must declare the headers it might access:

samples: [
  {
    params: { locale: "en-US", handle: "__placeholder__" },
    searchParams: { variant: "1" },
    cookies: [{ name: "shopify_cartId", value: null }],
    headers: [["x-vercel-ip-postal-code", null]], // ← add this
  },
],

null means "header may be absent." If you forget, the build error is explicit:

Error: Route "..." accessed header "x-vercel-ip-postal-code" which is not
       defined in the `samples` of `unstable_instant`. Add it to the
       sample's `headers` array, or `["...", null]` if it should be absent.

F. redirect() from next-intl doesn't return never

// BREAKS: TS doesn't narrow `session` after redirect
import { redirect } from "@/lib/i18n/navigation";
if (!session) redirect({ href: "/account/login", locale });
return session; // type error: session is CustomerSession | null

next-intl's redirect is typed to return void, so TypeScript doesn't treat it as control-flow-ending. Use next/navigation's redirect (which returns never) and prefix the locale yourself:

import { redirect } from "next/navigation";
import { getLocale } from "@/lib/params";
if (!session) redirect(`/${await getLocale()}/account/login`);
return session; // OK, narrowed

Step-by-step

Step 1: Routing config

Create lib/i18n/routing.ts:

import { defineRouting } from "next-intl/routing";
import { defaultLocale, enabledLocales } from ".";
export const routing = defineRouting({
  locales: enabledLocales, // pulled from lib/i18n/index.ts — never hardcode
  defaultLocale,
  localePrefix: "always",
});

Create lib/i18n/navigation.ts:

import { createNavigation } from "next-intl/navigation";
import { routing } from "./routing";
export const { Link, redirect, usePathname, useRouter } = createNavigation(routing);

Per "Cache Components compatibility C" above, Link here is mostly used by the locale switcher / programmatic routing in client components — not as a wholesale replacement for next/link.

Step 2: Move routes under app/[locale]/

Move every route file from app/ into app/[locale]/:

• app/layout.tsx → app/[locale]/layout.tsx (becomes the root layout for the locale segment). Delete the original `app/layout.tsx` after the move — see compatibility A above; both files cannot coexist.
• app/page.tsx, app/error.tsx, app/not-found.tsx → app/[locale]/...
• app/about/, app/account/, app/cart/, app/collections/, app/products/, app/search/ → app/[locale]/...

Stay at `app/`: api/, sitemap.ts, robots.ts, global-error.tsx, globals.css, favicon.ico.

In the moved layout, fix import "./globals.css" → import "../globals.css".

Update every PageProps<"/foo"> and LayoutProps<"/foo"> generic to include the locale segment: PageProps<"/[locale]/products/[handle]">, LayoutProps<"/[locale]">, etc.

Step 3: lib/params.ts reads from root params

import { notFound } from "next/navigation";
import { locale as rootLocale } from "next/root-params";
import { type Locale, locales } from "./i18n";
export async function getLocale(): Promise<Locale> {
  const current = await rootLocale();
  if (!current || !locales.includes(current as Locale)) notFound();
  return current as Locale;
}

Step 4: lib/i18n/request.ts loads messages by resolved locale

import { hasLocale } from "next-intl";
import { getRequestConfig } from "next-intl/server";
import { getLocale } from "../params";
import type enMessages from "./messages/en.json";
import { routing } from "./routing";
const messageLoaders: Record<string, () => Promise<{ default: typeof enMessages }>> = {
  "en-US": () => import("./messages/en.json"),
  // Add per-locale loaders as you ship message files. Missing locales fall
  // back to the default locale loader.
};
// We intentionally do NOT destructure `{ locale }` from the callback args.
// next-intl populates that arg from the `x-next-intl-locale` request header,
// and reading request headers from inside a cached tree forces the route
// dynamic — every `unstable_instant` sample then needs an explicit
// `headers: [["x-next-intl-locale", null]]` declaration. Going straight to
// `getLocale()` (which reads `next/root-params`) keeps the lookup cacheable.
export default getRequestConfig(async () => {
  const requested = await getLocale();
  const locale = hasLocale(routing.locales, requested) ? requested : routing.defaultLocale;
  const loader = messageLoaders[locale] ?? messageLoaders[routing.defaultLocale];
  const messages = (await loader()).default as typeof enMessages;
  return { locale, messages };
});

Step 5: proxy.ts middleware

import createMiddleware from "next-intl/middleware";
import { type NextRequest, NextResponse } from "next/server";
import { routing } from "@/lib/i18n/routing";
const handlei18n = createMiddleware(routing);
export default function middleware(request: NextRequest): NextResponse {
  const response = handlei18n(request);
  if (!response.ok) return response;
  const rewriteHeader = response.headers.get("x-middleware-rewrite");
  if (!rewriteHeader) return response;
  const rewriteTarget = new URL(rewriteHeader, request.url);
  const [, ...segments] = rewriteTarget.pathname.split("/");
  const normalized = new URL(`/${segments.filter(Boolean).join("/")}`, request.url);
  normalized.search = rewriteTarget.search;
  return NextResponse.rewrite(normalized, { headers: response.headers });
}
export const config = {
  matcher: ["/((?!api|_next|_vercel|.*\\..*).*)"],
};

The file is proxy.ts (Next.js 16 convention), not middleware.ts.

Step 6: Internal hrefs — keep next/link

Per the cache-components note above, leave existing `next/link` imports alone. Middleware redirects unprefixed URLs to the active locale on click. The only places to use the next-intl-aware Link are inside client components that explicitly need to switch locales (e.g. a locale switcher) — and even then, usePathname() + useRouter().push() from next/navigation plus a manual segment swap is often cleaner under cacheComponents.

For programmatic redirects in server code, use next/navigation's redirect:

redirect(`/${await getLocale()}/account/login`);

Step 7: lib/seo.ts — locale-aware canonicals + hreflang alternates

import { defaultLocale, enabledLocales } from "./i18n";
import { getLocale } from "./params";
function withLocalePath(locale: string, pathname: string): string {
  const normalized = normalizePath(pathname);
  return normalized === "/" ? `/${locale}` : `/${locale}${normalized}`;
}
export async function buildAlternates({ pathname, searchParams }: {...}): Promise<Metadata["alternates"]> {
  const locale = await getLocale();
  const canonical = buildCanonicalPath(withLocalePath(locale, pathname), searchParams);
  const languages: Record<string, string> = {};
  for (const candidate of enabledLocales) {
    languages[candidate] = buildCanonicalPath(withLocalePath(candidate, pathname), searchParams);
  }
  languages["x-default"] = buildCanonicalPath(withLocalePath(defaultLocale, pathname), searchParams);
  return { canonical, languages };
}

buildAlternates is now async — update every caller to await.

Step 8: Sitemap per-locale entries

import { enabledLocales } from "@/lib/i18n";
function localizePath(locale: string, pathname: string): string {
  if (pathname === "/") return `/${locale}`;
  const normalized = pathname.startsWith("/") ? pathname : `/${pathname}`;
  return `/${locale}${normalized}`;
}
// Inside sitemap(): one entry per locale per page.

Step 9: next.config.ts rewrites/redirects on /:locale/*

Existing markdown content-negotiation rewrites must move their source from /products/:handle to /:locale/products/:handle, etc. Destinations stay at /md/products/:handle, /md/collections/:handle, and /md/search — the handlers read locale from query params, not the URL path. Add the locale-prefixed redirect rules from the original config (/:locale/product* → /:locale/products*).

Step 10: app/(unlocalized)/page.tsx fallback

import { permanentRedirect } from "next/navigation";
import { defaultLocale } from "@/lib/i18n";
export default function UnlocalizedRoot(): never {
  permanentRedirect(`/${defaultLocale}`);
}

This is a defensive fallback; with localePrefix: "always" middleware should already redirect /.

Step 11: generateStaticParams on the locale layout

import { locales } from "@/lib/i18n";
export const generateStaticParams = async () => {
  return locales.map((locale) => ({ locale }));
};

Step 12: Patch unstable_instant samples

Walk every route file that exports unstable_instant and add locale to each sample's params:

params: { locale: "en-US", handle: "__placeholder__" }

If any layout-level server component (e.g. a shipping/postal banner, geo-aware nav) reads headers(), also add a headers array to every sample:

headers: [["x-vercel-ip-postal-code", null]]

(See "Cache Components compatibility D/E" at the top.)

Step 13: (Conditional) Re-enable LocaleCurrencySelector in the megamenu

Only if the enable-shopify-menus skill has already been run and components/nav/megamenu/index.tsx exists. The selector component lives at components/nav/locale-currency.tsx (with a fallback at locale-currency-fallback.tsx). Wire it into both MegamenuDesktop and MegamenuMobile per the original instructions.

Verifying

After applying:

pnpm build         # should pass; routes prerender at /en-US, /en-GB, etc.
pnpm dev           # then:
curl -I /          # → 307 /en-US
curl -I /products  # → 307 /en-US/products
curl /sitemap.xml  # → entries with /en-US/... URLs
curl /en-US        # → 200 with <html lang="en-US">

Smoke-test checklist:

• [ ] Build passes
• [ ] Bare / redirects to default locale
• [ ] Each enabled locale serves 200 at its prefix
• [ ] <html lang> matches the URL's locale segment
• [ ] Sitemap emits one entry per locale per page
• [ ] Canonical + hreflang alternates appear in page metadata
• [ ] Unprefixed internal links from existing next/link calls redirect (one extra hop, but correct)