From e58132c4737fffe74d2e6ebdd724e219bc03e088 Mon Sep 17 00:00:00 2001
From: hammadxcm <hammadkhanxcm@gmail.com>
Date: Thu, 23 Apr 2026 18:32:16 +0500
Subject: [PATCH 1/2] fix(i18n): use correct defaultLocale when domains array
 is present on default host

When a `domains` array is configured in i18n and the request is served
from the default domain (e.g., localhost), `defaultLocale` was
incorrectly set to a configured domain's value because
`detectDomainLocale` matched on the detected locale rather than
hostname. Remove `domainLocale?.defaultLocale` from the fallback chain
in `RouteModule.prepare()` since `base-server.ts` already sets the
correct value in request metadata via hostname-only matching.

Fixes #90131
---
 .../src/server/route-modules/route-module.ts  |  4 +-
 test/e2e/i18n-support/shared.ts               | 37 +++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/packages/next/src/server/route-modules/route-module.ts b/packages/next/src/server/route-modules/route-module.ts
index 1159e775f175..9fab5d280911 100644
--- a/packages/next/src/server/route-modules/route-module.ts
+++ b/packages/next/src/server/route-modules/route-module.ts
@@ -763,9 +763,7 @@ export abstract class RouteModule<
     }
 
     const defaultLocale =
-      getRequestMeta(req, 'defaultLocale') ||
-      domainLocale?.defaultLocale ||
-      i18n?.defaultLocale
+      getRequestMeta(req, 'defaultLocale') || i18n?.defaultLocale
 
     // Ensure parsedUrl.pathname includes locale before processing
     // rewrites or they won't match correctly.
diff --git a/test/e2e/i18n-support/shared.ts b/test/e2e/i18n-support/shared.ts
index c371ee3fd321..2b492fd07f22 100644
--- a/test/e2e/i18n-support/shared.ts
+++ b/test/e2e/i18n-support/shared.ts
@@ -2645,6 +2645,43 @@ export function runTests(ctx) {
     expect(JSON.parse($2('#router-locales').text())).toEqual(locales)
   })
 
+  it('should not use domain defaultLocale when visiting domain locale on default host', async () => {
+    // Visit /go/another on localhost (no host header matching a configured domain)
+    // defaultLocale should be en-US (main config), not go (example.com domain)
+    const res = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath}/go/another`,
+      undefined,
+      {
+        redirect: 'manual',
+      }
+    )
+
+    expect(res.status).toBe(200)
+    const html = await res.text()
+    const $ = cheerio.load(html)
+    expect($('#router-locale').text()).toBe('go')
+    expect($('#router-default-locale').text()).toBe('en-US')
+    expect(JSON.parse($('#props').text()).defaultLocale).toBe('en-US')
+
+    // Also test with the other domain locale (do)
+    const res2 = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath}/do/another`,
+      undefined,
+      {
+        redirect: 'manual',
+      }
+    )
+
+    expect(res2.status).toBe(200)
+    const html2 = await res2.text()
+    const $2 = cheerio.load(html2)
+    expect($2('#router-locale').text()).toBe('do')
+    expect($2('#router-default-locale').text()).toBe('en-US')
+    expect(JSON.parse($2('#props').text()).defaultLocale).toBe('en-US')
+  })
+
   it('should not strip locale prefix for default locale with locale domains', async () => {
     const res = await fetchViaHTTP(
       ctx.appPort,

From 1dc69675c86568d4ecea89529cf9ff671116544f Mon Sep 17 00:00:00 2001
From: hammadxcm <hammadkhanxcm@gmail.com>
Date: Tue, 26 May 2026 23:03:13 +0500
Subject: [PATCH 2/2] test(i18n): cover domain secondary-locale match branch on
 default host

Adds /go-BE and /do-BE cases that exercise the item.locales match branch
of detectDomainLocale (distinct from the defaultLocale match), verifying
the request defaultLocale stays en-US on the default host.
---
 test/e2e/i18n-support/shared.ts | 39 +++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/test/e2e/i18n-support/shared.ts b/test/e2e/i18n-support/shared.ts
index 2b492fd07f22..615e71160e34 100644
--- a/test/e2e/i18n-support/shared.ts
+++ b/test/e2e/i18n-support/shared.ts
@@ -2682,6 +2682,45 @@ export function runTests(ctx) {
     expect(JSON.parse($2('#props').text()).defaultLocale).toBe('en-US')
   })
 
+  it("should not use domain defaultLocale when visiting a domain's secondary locale on default host", async () => {
+    // `go-BE`/`do-BE` are not a domain's defaultLocale; they only appear in a
+    // domain's `locales` array. This exercises the `item.locales` match branch
+    // of detectDomainLocale (distinct from the defaultLocale match above), and
+    // the request's defaultLocale should still be en-US (main config).
+    const res = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath}/go-BE/another`,
+      undefined,
+      {
+        redirect: 'manual',
+      }
+    )
+
+    expect(res.status).toBe(200)
+    const html = await res.text()
+    const $ = cheerio.load(html)
+    expect($('#router-locale').text()).toBe('go-BE')
+    expect($('#router-default-locale').text()).toBe('en-US')
+    expect(JSON.parse($('#props').text()).defaultLocale).toBe('en-US')
+
+    // Also test with the other domain's secondary locale (do-BE)
+    const res2 = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath}/do-BE/another`,
+      undefined,
+      {
+        redirect: 'manual',
+      }
+    )
+
+    expect(res2.status).toBe(200)
+    const html2 = await res2.text()
+    const $2 = cheerio.load(html2)
+    expect($2('#router-locale').text()).toBe('do-BE')
+    expect($2('#router-default-locale').text()).toBe('en-US')
+    expect(JSON.parse($2('#props').text()).defaultLocale).toBe('en-US')
+  })
+
   it('should not strip locale prefix for default locale with locale domains', async () => {
     const res = await fetchViaHTTP(
       ctx.appPort,