domain progress with hydrating link

packages/next-intl/src/navigation/createNavigation.test.tsx

@@ -40,8 +40,15 @@ function mockCurrentLocale(locale: string) {
   }));
 }
 
+function mockLocation(location: Partial<typeof window.location>) {
+  delete (global.window as any).location;
+  global.window ??= Object.create(window);
+  (global.window as any).location = location;
+}
+
 beforeEach(() => {
   mockCurrentLocale('en');
+  mockLocation({host: 'localhost:3000'});
 });
 
 const locales = ['en', 'de', 'ja'] as const;
@@ -133,7 +140,7 @@ describe.each([
         expect(markup).toContain('hrefLang="de"');
       });
 
-      it('renders an object href', () => {
+      it('renders an object href with an external host', () => {
         render(
           <Link
             href={{
@@ -699,6 +706,33 @@ describe.each([
         expect(markup).toContain('href="/en/about"');
       });
 
+      it('does not render a prefix eventually on the client side for the default locale of the given domain', () => {
+        mockLocation({host: 'example.com'});
+        render(<Link href="/about">About</Link>);
+        expect(
+          screen.getByRole('link', {name: 'About'}).getAttribute('href')
+        ).toBe('/about');
+      });
+
+      it('renders a prefix when currently on a secondary locale', () => {
+        mockLocation({host: 'example.de'});
+        mockCurrentLocale('en');
+        render(<Link href="/about">About</Link>);
+        expect(
+          screen.getByRole('link', {name: 'About'}).getAttribute('href')
+        ).toBe('/en/about');
+      });
+
+      it('renders a prefix when currently on a secondary locale and linking to the default locale', () => {
+        mockLocation({host: 'example.de'});
+        mockCurrentLocale('en');
+        const markup = renderToString(
+          <Link href="/about" locale="de">
+            About
+          </Link>
+        );
+        expect(markup).toContain('href="/de/about"');
+      });
     });
 
     describe('getPathname', () => {

packages/next-intl/src/navigation/shared/BaseLink.tsx

@@ -2,23 +2,42 @@
 
 import NextLink from 'next/link';
 import {usePathname} from 'next/navigation';
-import React, {ComponentProps, MouseEvent} from 'react';
+import React, {ComponentProps, MouseEvent, useEffect, useState} from 'react';
 import useLocale from '../../react-client/useLocale';
 import syncLocaleCookie from './syncLocaleCookie';
 
 type Props = Omit<ComponentProps<typeof NextLink>, 'locale'> & {
   locale?: string;
   nodeRef?: ComponentProps<typeof NextLink>['ref'];
+  unprefixConfig?: {
+    domains: {[defaultLocale: string]: string};
+    pathname: string;
+  };
 };
 
-function BaseLink({href, locale, nodeRef, onClick, prefetch, ...rest}: Props) {
+export default function BaseLink({
+  href,
+  locale,
+  nodeRef,
+  onClick,
+  prefetch,
+  unprefixConfig,
+  ...rest
+}: Props) {
+  const curLocale = useLocale();
+  const isChangingLocale = locale !== curLocale;
+  const linkLocale = locale || curLocale;
+
+  const host = useHost();
+  const finalHref =
+    unprefixConfig && unprefixConfig.domains[linkLocale] === host
+      ? unprefixConfig.pathname
+      : href;
+
   // The types aren't entirely correct here. Outside of Next.js
   // `useParams` can be called, but the return type is `null`.
   const pathname = usePathname() as ReturnType<typeof usePathname> | null;
 
-  const curLocale = useLocale();
-  const isChangingLocale = locale !== curLocale;
-
   function onLinkClick(event: MouseEvent<HTMLAnchorElement>) {
     syncLocaleCookie(pathname, curLocale, locale);
     if (onClick) onClick(event);
@@ -36,7 +55,7 @@ function BaseLink({href, locale, nodeRef, onClick, prefetch, ...rest}: Props) {
   return (
     <NextLink
       ref={nodeRef}
-      href={href}
+      href={finalHref}
       hrefLang={isChangingLocale ? locale : undefined}
       onClick={onLinkClick}
       prefetch={prefetch}
@@ -45,4 +64,12 @@ function BaseLink({href, locale, nodeRef, onClick, prefetch, ...rest}: Props) {
   );
 }
 
-export default BaseLink;
+function useHost() {
+  const [host, setHost] = useState<string>();
+
+  useEffect(() => {
+    setHost(window.location.host);
+  }, []);
+
+  return host;
+}

packages/next-intl/src/navigation/shared/createSharedNavigationFns.tsx

@@ -9,7 +9,7 @@ import {
   RoutingConfigLocalizedNavigation,
   RoutingConfigSharedNavigation
 } from '../../routing/config';
-import {Locales, Pathnames} from '../../routing/types';
+import {DomainConfig, Locales, Pathnames} from '../../routing/types';
 import {ParametersExceptFirst} from '../../shared/types';
 import {isLocalizableHref} from '../../shared/utils';
 import BaseLink from './BaseLink';
@@ -60,7 +60,8 @@ export default function createSharedNavigationFns<
   // that the user might get redirected again if the middleware detects that the
   // prefix is not needed.
   const forcePrefixSsr =
-    config.localePrefix.mode === 'as-needed' && 'domains' in config;
+    (config.localePrefix.mode === 'as-needed' && 'domains' in config) ||
+    undefined;
 
   type LinkProps<Pathname extends keyof AppPathnames = never> = Omit<
     ComponentProps<typeof BaseLink>,
@@ -85,17 +86,18 @@ export default function createSharedNavigationFns<
       pathname = href;
     }
 
-    const curLocale = getLocale();
-
     // @ts-expect-error -- This is ok
-    const finalPathname = isLocalizableHref(href)
+    const isLocalizable = isLocalizableHref(href);
+
+    const curLocale = getLocale();
+    const finalPathname = isLocalizable
       ? getPathname(
           {
             locale: locale || curLocale,
             // @ts-expect-error -- This is ok
             href: pathnames == null ? pathname : {pathname, params}
           },
-          locale != null || forcePrefixSsr
+          locale != null || forcePrefixSsr || undefined
         )
       : pathname;
 
@@ -107,6 +109,33 @@ export default function createSharedNavigationFns<
           pathname: finalPathname
         }}
         locale={locale}
+        // Provide the minimal relevant information to the client side in order
+        // to potentially remove the prefix in case of the `forcePrefixSsr` case
+        unprefixConfig={
+          forcePrefixSsr && isLocalizable
+            ? {
+                domains: (config as any).domains.reduce(
+                  (
+                    acc: Record<Locale, string>,
+                    domain: DomainConfig<AppLocales>
+                  ) => {
+                    // @ts-expect-error -- This is ok
+                    acc[domain.defaultLocale] = domain.domain;
+                    return acc;
+                  },
+                  {}
+                ),
+                pathname: getPathname(
+                  {
+                    locale: curLocale,
+                    // @ts-expect-error -- This is ok
+                    href: pathnames == null ? pathname : {pathname, params}
+                  },
+                  false
+                )
+              }
+            : undefined
+        }
         {...rest}
       />
     );

packages/next-intl/src/navigation/shared/utils.tsx

@@ -228,8 +228,10 @@ export function applyPathnamePrefix<AppLocales extends Locales>(
   const {mode} = routing.localePrefix;
 
   let shouldPrefix;
-  if (isLocalizableHref(pathname)) {
-    if (force || mode === 'always') {
+  if (force !== undefined) {
+    shouldPrefix = force;
+  } else if (isLocalizableHref(pathname)) {
+    if (mode === 'always') {
       shouldPrefix = true;
     } else if (mode === 'as-needed') {
       let {defaultLocale} = routing;