I18N: Add JavaScript translation support.

Adds the `wp_set_script_translations()` function which registers translations for a JavaScript file. This function takes a handle, domain and optionally a path and ensures JavaScript translation files are loaded if they exist.

Merges [43825,43828,43859,43898] from the 5.0 branch to trunk.

Props herregroen, atimmer, omarreiss, nerrad, swissspidy, ocean90, georgestephanis.
Fixes #45103, #45256.



git-svn-id: https://develop.svn.wordpress.org/trunk@44169 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-dependency.php

@@ -67,6 +67,22 @@ class _WP_Dependency {
 	 */
 	public $extra = array();
 
+	/**
+	 * Translation textdomain set for this dependency.
+	 *
+	 * @since 5.0.0
+	 * @var string
+	 */
+	public $textdomain;
+
+	/**
+	 * Translation path set for this dependency.
+	 *
+	 * @since 5.0.0
+	 * @var string
+	 */
+	public $translations_path;
+
 	/**
 	 * Setup dependencies.
 	 *
@@ -96,4 +112,12 @@ class _WP_Dependency {
 		return true;
 	}
 
+	public function set_translations( $domain, $path = null ) {
+		if ( ! is_string( $domain ) ) {
+			return false;
+		}
+		$this->textdomain        = $domain;
+		$this->translations_path = $path;
+		return true;
+	}
 }