REST API: Render response in user locale with ?_locale=user.

Introduces new `determine_locale()` function for deciding the proper locale to use for a response. Default value is `get_user_locale()` in the admin, and `get_locale()` on the frontend. Because REST API requests are considered frontend requests, `?_locale=user` can be used to render the response in the user's locale.

Also updates `wp-login.php?wp_lang` implementation to benefit from this abstraction.

Merges [43776] from the 5.0 branch to trunk.

Props flixos90, mnelson4, swissspidy, TimothyBlynJacobs.
Fixes #44758.

Built from https://develop.svn.wordpress.org/trunk@44134


git-svn-id: http://core.svn.wordpress.org/trunk@43964 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-locale-switcher.php

@@ -45,7 +45,7 @@ class WP_Locale_Switcher {
 	 * @since 4.7.0
 	 */
 	public function __construct() {
-		$this->original_locale     = is_admin() ? get_user_locale() : get_locale();
+		$this->original_locale     = determine_locale();
 		$this->available_languages = array_merge( array( 'en_US' ), get_available_languages() );
 	}
 
@@ -69,7 +69,7 @@ class WP_Locale_Switcher {
 	 * @return bool True on success, false on failure.
 	 */
 	public function switch_to_locale( $locale ) {
-		$current_locale = is_admin() ? get_user_locale() : get_locale();
+		$current_locale = determine_locale();
 		if ( $current_locale === $locale ) {
 			return false;
 		}

wp-includes/general-template.php

@@ -718,7 +718,7 @@ function get_bloginfo( $show = '', $filter = 'raw' ) {
 			 */
 			$output = __( 'html_lang_attribute' );
 			if ( 'html_lang_attribute' === $output || preg_match( '/[^a-zA-Z0-9-]/', $output ) ) {
-				$output = is_admin() ? get_user_locale() : get_locale();
+				$output = determine_locale();
 				$output = str_replace( '_', '-', $output );
 			}
 			break;

wp-includes/l10n.php

@@ -104,6 +104,54 @@ function get_user_locale( $user_id = 0 ) {
 	return $locale ? $locale : get_locale();
 }
 
+/**
+ * Determine the current locale desired for the request.
+ *
+ * @since 5.0.0
+ *
+ * @global string $pagenow
+ *
+ * @return string The determined locale.
+ */
+function determine_locale() {
+	/**
+	 * Filters the locale for the current request prior to the default determination process.
+	 *
+	 * Using this filter allows to override the default logic, effectively short-circuiting the function.
+	 *
+	 * @since 5.0.0
+	 *
+	 * @param string|null The locale to return and short-circuit, or null as default.
+	 */
+	$determined_locale = apply_filters( 'pre_determine_locale', null );
+	if ( ! empty( $determined_locale ) && is_string( $determined_locale ) ) {
+		return $determined_locale;
+	}
+
+	$determined_locale = get_locale();
+
+	if ( is_admin() ) {
+		$determined_locale = get_user_locale();
+	}
+
+	if ( isset( $_GET['_locale'] ) && 'user' === $_GET['_locale'] && wp_is_json_request() && is_user_logged_in() ) {
+		$determined_locale = get_user_locale();
+	}
+
+	if ( ! empty( $_GET['wp_lang'] ) && 'wp-login.php' === $GLOBALS['pagenow'] ) {
+		$determined_locale = sanitize_text_field( $_GET['wp_lang'] );
+	}
+
+	/**
+	 * Filters the locale for the current request.
+	 *
+	 * @since 5.0.0
+	 *
+	 * @param string $locale The locale.
+	 */
+	return apply_filters( 'determine_locale', $determined_locale );
+}
+
 /**
  * Retrieve the translation of $text.
  *
@@ -685,7 +733,7 @@ function unload_textdomain( $domain ) {
  */
 function load_default_textdomain( $locale = null ) {
 	if ( null === $locale ) {
-		$locale = is_admin() ? get_user_locale() : get_locale();
+		$locale = determine_locale();
 	}
 
 	// Unload previously loaded strings so we can switch translations.
@@ -734,7 +782,7 @@ function load_plugin_textdomain( $domain, $deprecated = false, $plugin_rel_path
 	 * @param string $locale The plugin's current locale.
 	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
 	 */
-	$locale = apply_filters( 'plugin_locale', is_admin() ? get_user_locale() : get_locale(), $domain );
+	$locale = apply_filters( 'plugin_locale', determine_locale(), $domain );
 
 	$mofile = $domain . '-' . $locale . '.mo';
 
@@ -768,7 +816,7 @@ function load_plugin_textdomain( $domain, $deprecated = false, $plugin_rel_path
  */
 function load_muplugin_textdomain( $domain, $mu_plugin_rel_path = '' ) {
 	/** This filter is documented in wp-includes/l10n.php */
-	$locale = apply_filters( 'plugin_locale', is_admin() ? get_user_locale() : get_locale(), $domain );
+	$locale = apply_filters( 'plugin_locale', determine_locale(), $domain );
 
 	$mofile = $domain . '-' . $locale . '.mo';
 
@@ -807,7 +855,7 @@ function load_theme_textdomain( $domain, $path = false ) {
 	 * @param string $locale The theme's current locale.
 	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
 	 */
-	$locale = apply_filters( 'theme_locale', is_admin() ? get_user_locale() : get_locale(), $domain );
+	$locale = apply_filters( 'theme_locale', determine_locale(), $domain );
 
 	$mofile = $domain . '-' . $locale . '.mo';
 
@@ -941,7 +989,7 @@ function _get_path_to_translation_from_lang_dir( $domain ) {
 		}
 	}
 
-	$locale = is_admin() ? get_user_locale() : get_locale();
+	$locale = determine_locale();
 	$mofile = "{$domain}-{$locale}.mo";
 
 	$path = WP_LANG_DIR . '/plugins/' . $mofile;

wp-includes/script-loader.php

@@ -954,7 +954,7 @@ function wp_default_scripts( &$scripts ) {
 			'var mejsL10n = %s;',
 			wp_json_encode(
 				array(
-					'language' => strtolower( strtok( is_admin() ? get_user_locale() : get_locale(), '_-' ) ),
+					'language' => strtolower( strtok( determine_locale(), '_-' ) ),
 					'strings'  => array(
 						'mejs.install-flash'       => __( 'You are using a browser that does not have Flash player enabled or installed. Please turn on your Flash player plugin or download the latest version from https://get.adobe.com/flashplayer/' ),
 						'mejs.fullscreen-off'      => __( 'Turn off Fullscreen' ),

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44133';
+$wp_version = '5.1-alpha-44134';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-login.php

@@ -464,9 +464,6 @@ if ( SITECOOKIEPATH != COOKIEPATH ) {
 	setcookie( TEST_COOKIE, 'WP Cookie check', 0, SITECOOKIEPATH, COOKIE_DOMAIN, $secure );
 }
 
-$lang            = ! empty( $_GET['wp_lang'] ) ? sanitize_text_field( $_GET['wp_lang'] ) : '';
-$switched_locale = switch_to_locale( $lang );
-
 /**
  * Fires when the login form is initialized.
  *
@@ -527,10 +524,6 @@ switch ( $action ) {
 		}
 		setcookie( 'wp-postpass_' . COOKIEHASH, $hasher->HashPassword( wp_unslash( $_POST['post_password'] ) ), $expire, COOKIEPATH, COOKIE_DOMAIN, $secure );
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		wp_safe_redirect( wp_get_referer() );
 		exit();
 
@@ -548,10 +541,6 @@ switch ( $action ) {
 			$requested_redirect_to = '';
 		}
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		/**
 		 * Filters the log out redirect URL.
 		 *
@@ -649,10 +638,6 @@ switch ( $action ) {
 		<?php
 		login_footer( 'user_login' );
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		break;
 
 	case 'resetpass':
@@ -780,10 +765,6 @@ switch ( $action ) {
 		<?php
 		login_footer( 'user_pass' );
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		break;
 
 	case 'register':
@@ -867,10 +848,6 @@ switch ( $action ) {
 		<?php
 		login_footer( 'user_login' );
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		break;
 
 	case 'confirmaction':
@@ -1179,9 +1156,5 @@ switch ( $action ) {
 		<?php
 		login_footer();
 
-		if ( $switched_locale ) {
-			restore_previous_locale();
-		}
-
 		break;
 } // End action switch.