Ensure i18n + API rewrite is handled correctly

packages/next/next-server/server/next-server.ts

@@ -908,7 +908,7 @@ export default class Server {
       match: route('/:path*'),
       type: 'route',
       name: 'Catchall render',
-      fn: async (req, res, params, parsedUrl) => {
+      fn: async (req, res, _params, parsedUrl) => {
         let { pathname, query } = parsedUrl
         if (!pathname) {
           throw new Error('pathname is undefined')
@@ -929,7 +929,7 @@ export default class Server {
           }
         }
 
-        if (params?.path?.[0] === 'api') {
+        if (pathname === '/api' || pathname.startsWith('/api/')) {
           const handled = await this.handleApiRequest(
             req as NextApiRequest,
             res as NextApiResponse,
@@ -1045,6 +1045,9 @@ export default class Server {
     const pageModule = await require(builtPagePath)
     query = { ...query, ...params }
 
+    delete query.__nextLocale
+    delete query.__nextDefaultLocale
+
     if (!this.renderOpts.dev && this._isLikeServerless) {
       if (typeof pageModule.default === 'function') {
         prepareServerlessUrl(req, query)

test/integration/i18n-support-base-path/next.config.js

@@ -82,6 +82,10 @@ module.exports = {
         source: '/rewrite-5',
         destination: 'http://localhost:__EXTERNAL_PORT__',
       },
+      {
+        source: '/sitemap.xml',
+        destination: '/api/hello',
+      },
     ]
   },
   async headers() {

test/integration/i18n-support/next.config.js

@@ -83,6 +83,10 @@ module.exports = {
         source: '/rewrite-5',
         destination: 'http://localhost:__EXTERNAL_PORT__',
       },
+      {
+        source: '/sitemap.xml',
+        destination: '/api/hello',
+      },
     ]
   },
   async headers() {

test/integration/i18n-support/test/shared.js

@@ -670,6 +670,71 @@ export function runTests(ctx) {
     }
   })
 
+  it('should visit API route directly correctly', async () => {
+    for (const locale of locales) {
+      const res = await fetchViaHTTP(
+        ctx.appPort,
+        `${ctx.basePath || ''}${
+          locale === 'en-US' ? '' : `/${locale}`
+        }/api/hello`,
+        undefined,
+        {
+          redirect: 'manual',
+        }
+      )
+
+      const data = await res.json()
+      expect(data).toEqual({
+        hello: true,
+        query: {},
+      })
+    }
+  })
+
+  it('should visit dynamic API route directly correctly', async () => {
+    for (const locale of locales) {
+      const res = await fetchViaHTTP(
+        ctx.appPort,
+        `${ctx.basePath || ''}${
+          locale === 'en-US' ? '' : `/${locale}`
+        }/api/post/first`,
+        undefined,
+        {
+          redirect: 'manual',
+        }
+      )
+
+      const data = await res.json()
+      expect(data).toEqual({
+        post: true,
+        query: {
+          slug: 'first',
+        },
+      })
+    }
+  })
+
+  it('should rewrite to API route correctly', async () => {
+    for (const locale of locales) {
+      const res = await fetchViaHTTP(
+        ctx.appPort,
+        `${ctx.basePath || ''}${
+          locale === 'en-US' ? '' : `/${locale}`
+        }/sitemap.xml`,
+        undefined,
+        {
+          redirect: 'manual',
+        }
+      )
+
+      const data = await res.json()
+      expect(data).toEqual({
+        hello: true,
+        query: {},
+      })
+    }
+  })
+
   it('should apply rewrites correctly', async () => {
     let res = await fetchViaHTTP(
       ctx.appPort,