Fix incorrect directory to load text domain (#5040)

#5038

lib/i18n.php

@@ -53,7 +53,7 @@ function gutenberg_load_plugin_textdomain() {
 	load_plugin_textdomain(
 		'gutenberg',
 		false,
-		dirname( plugin_basename( __FILE__ ) ) . '/languages/'
+		plugin_basename( gutenberg_dir_path() ) . '/languages/'
 	);
 }
 add_action( 'plugins_loaded', 'gutenberg_load_plugin_textdomain' );

phpunit/class-i18n-functions-test.php

@@ -0,0 +1,32 @@
+<?php
+/**
+ * Tests for i18n functions
+ *
+ * @package Gutenberg
+ */
+class I18n_Functions_Test extends WP_UnitTestCase {
+
+	/**
+	 * @test
+	 * @group #5038
+	 * @covers gutenberg_load_plugin_textdomain
+	 */
+	public function it_should_load_language_files_from_gutenberg_languages() {
+		if ( 'gutenberg' !== plugin_basename( gutenberg_dir_path() ) ) {
+			$this->markTestSkipped( 'The path is not matching in docker test environment. Needs further investigation.' );
+			return;
+		}
+
+		add_action( 'load_textdomain', array( $this, 'check_arguments_in_load_textdomaincheck' ), 10, 2 );
+		gutenberg_load_plugin_textdomain();
+	}
+
+	public function check_arguments_in_load_textdomaincheck( $domain, $mofile ) {
+		$content_language_file_pattern = 'languages[\\/]plugins[\\/]gutenberg-[a-z]{2}_[A-Z]{2}.mo$';
+		$plugin_language_file_pattern  = 'gutenberg[\\/]languages[\\/]gutenberg-[a-z]{2}_[A-Z]{2}.mo$';
+		$regex_pattern                 = '#' . $content_language_file_pattern . '|' . $plugin_language_file_pattern . '#';
+
+		$this->assertEquals( 'gutenberg', $domain );
+		$this->assertRegExp( $regex_pattern, $mofile );
+	}
+}