Ensure API routes are not available under the locale

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

@@ -465,6 +465,13 @@ export default class Server {
           pathname: localePathResult.pathname,
         })
         ;(req as any).__nextStrippedLocale = true
+
+        if (
+          localePathResult.pathname === '/api' ||
+          localePathResult.pathname.startsWith('/api/')
+        ) {
+          return this.render404(req, res, parsedUrl)
+        }
       }
 
       // If a detected locale is a domain specific locale and we aren't already

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

@@ -37,7 +37,7 @@ async function addDefaultLocaleCookie(browser) {
 }
 
 export function runTests(ctx) {
-  it.only('should have domainLocales available on useRouter', async () => {
+  it('should have domainLocales available on useRouter', async () => {
     const browser = await webdriver(ctx.appPort, `${ctx.basePath || '/'}`)
     expect(
       JSON.parse(await browser.elementByCss('#router-domain-locales').text())
@@ -1146,44 +1146,54 @@ export function runTests(ctx) {
     for (const locale of locales) {
       const res = await fetchViaHTTP(
         ctx.appPort,
-        `${ctx.basePath || ''}${
-          locale === 'en-US' ? '' : `/${locale}`
-        }/api/hello`,
+        `${ctx.basePath || ''}/${locale}/api/hello`,
         undefined,
         {
           redirect: 'manual',
         }
       )
 
-      const data = await res.json()
-      expect(data).toEqual({
-        hello: true,
-        query: {},
-      })
+      expect(res.status).toBe(404)
     }
+
+    const res = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath || ''}/api/hello`
+    )
+
+    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' ? '' : `/${locale}`
-        }/api/post/first`,
+        `${ctx.basePath || ''}/${locale}/api/post/first`,
         undefined,
         {
           redirect: 'manual',
         }
       )
 
-      const data = await res.json()
-      expect(data).toEqual({
-        post: true,
-        query: {
-          slug: 'first',
-        },
-      })
+      expect(res.status).toBe(404)
     }
+
+    const res = await fetchViaHTTP(
+      ctx.appPort,
+      `${ctx.basePath || ''}/api/post/first`
+    )
+
+    const data = await res.json()
+    expect(data).toEqual({
+      post: true,
+      query: {
+        slug: 'first',
+      },
+    })
   })
 
   it('should rewrite to API route correctly', async () => {