Add user locale api-fetch middleware

See #10811

packages/api-fetch/src/index.js

@@ -12,6 +12,7 @@ import createPreloadingMiddleware from './middlewares/preloading';
 import fetchAllMiddleware from './middlewares/fetch-all-middleware';
 import namespaceEndpointMiddleware from './middlewares/namespace-endpoint';
 import httpV1Middleware from './middlewares/http-v1';
+import userLocaleMiddleware from './middlewares/user-locale';
 
 const middlewares = [];
 
@@ -109,6 +110,7 @@ function apiFetch( options ) {
 		fetchAllMiddleware,
 		httpV1Middleware,
 		namespaceEndpointMiddleware,
+		userLocaleMiddleware,
 		...middlewares,
 	].reverse();
 

packages/api-fetch/src/middlewares/test/user-locale.js

@@ -0,0 +1,66 @@
+/**
+ * Internal dependencies
+ */
+import userLocaleMiddleware from '../user-locale';
+
+describe( 'User locale middleware', () => {
+	it( 'should append the _locale parameter to the path', () => {
+		expect.hasAssertions();
+
+		const requestOptions = {
+			method: 'GET',
+			path: '/wp/v2/posts',
+		};
+
+		const callback = ( options ) => {
+			expect( options.path ).toBe( '/wp/v2/posts?_locale=user' );
+		};
+
+		userLocaleMiddleware( requestOptions, callback );
+	} );
+
+	it( 'should append the _locale parameter to path with existing query argument', () => {
+		expect.hasAssertions();
+
+		const requestOptions = {
+			method: 'GET',
+			path: '/wp/v2/posts?foo=bar',
+		};
+
+		const callback = ( options ) => {
+			expect( options.path ).toBe( '/wp/v2/posts?foo=bar&_locale=user' );
+		};
+
+		userLocaleMiddleware( requestOptions, callback );
+	} );
+
+	it( 'should append the _locale parameter to the url', () => {
+		expect.hasAssertions();
+
+		const requestOptions = {
+			method: 'GET',
+			url: 'http://wp.org/wp-json/wp/v2/posts',
+		};
+
+		const callback = ( options ) => {
+			expect( options.url ).toBe( 'http://wp.org/wp-json/wp/v2/posts?_locale=user' );
+		};
+
+		userLocaleMiddleware( requestOptions, callback );
+	} );
+
+	it( 'should append the _locale parameter to url with existing query argument', () => {
+		expect.hasAssertions();
+
+		const requestOptions = {
+			method: 'GET',
+			url: 'http://wp.org/wp-json/wp/v2/posts?foo=bar',
+		};
+
+		const callback = ( options ) => {
+			expect( options.url ).toBe( 'http://wp.org/wp-json/wp/v2/posts?foo=bar&_locale=user' );
+		};
+
+		userLocaleMiddleware( requestOptions, callback );
+	} );
+} );

packages/api-fetch/src/middlewares/user-locale.js

@@ -0,0 +1,21 @@
+function userLocaleMiddleware( options, next ) {
+	if ( typeof options.url === 'string' ) {
+		if ( -1 !== options.url.indexOf( '?' ) ) {
+			options.url += '&_locale=user';
+		} else {
+			options.url += '?_locale=user';
+		}
+	}
+
+	if ( typeof options.path === 'string' ) {
+		if ( -1 !== options.path.indexOf( '?' ) ) {
+			options.path += '&_locale=user';
+		} else {
+			options.path += '?_locale=user';
+		}
+	}
+
+	return next( options, next );
+}
+
+export default userLocaleMiddleware;