Flush rewrite rules when language changed or translation updated

changelog/fix-404-after-language-switch

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Flush rewrite rules when the website language was changed or the translation was updated.

includes/class-sensei.php

@@ -434,13 +434,47 @@
 		// Localisation
 		$this->load_plugin_textdomain();
 		add_action( 'init', array( $this, 'load_localisation' ), 0 );
+		add_action( 'update_option_WPLANG', array( $this, 'maybe_initiate_rewrite_rules_flush_after_language_change' ), 10, 2 );
+		add_action( 'upgrader_process_complete', array( $this, 'maybe_initiate_rewrite_rules_flush_on_translation_update' ), 10, 2 );
 
 		$this->initialize_cache_groups();
 		$this->initialize_global_objects();
 		$this->initialize_cli();
 		$this->initialize_3rd_party_compatibility();
 	}
 
+	/**
+	 * Maybe initiate rewrite rules flush when WordPress language has been changed.
+	 *
+	 * @internal
+	 *
+	 * @since $$next-version$$
+	 *
+	 * @param mixed $old_value Old value.
+	 * @param mixed $new_value New value.
+	 */
+	public function maybe_initiate_rewrite_rules_flush_after_language_change( $old_value, $new_value ) {
+		if ( $old_value !== $new_value ) {
+			$this->initiate_rewrite_rules_flush();
+		}
+	}
+
+	/**
+	 * Maybe initiate rewrite rules flush when WordPress translation has been updated.
+	 *
+	 * @internal
+	 *
+	 * @since $$next-version$$
+	 *
+	 * @param WP_Upgrader $upgrader_object Upgrader object.
+	 * @param array       $options Options.
+	 */
+	public function maybe_initiate_rewrite_rules_flush_on_translation_update( $upgrader_object, $options ) {
+		if ( 'translation' === $options['type'] ) {
+			$this->initiate_rewrite_rules_flush();
+		}
+	}
+
 	/**
 	 * Global Sensei Instance
 	 *

tests/unit-tests/test-class-sensei.php

@@ -210,6 +210,70 @@ public function testConstructor_Always_InitializesClockProperty() {
 		$this->assertInstanceOf( Clock_Interface::class, $sensei->clock );
 	}
 
+	public function testConstruct_Always_AddsActionOnUpdateOptionWplang() {
+		/* Arrange. */
+		$sensei = Sensei();
+
+		/* Assert. */
+		$this->assertSame( 10, has_action( 'update_option_WPLANG', [ $sensei, 'maybe_initiate_rewrite_rules_flush_after_language_change' ] ) );
+	}
+
+	public function testConstruct_Always_AddsActionOnUpgraderProcessComplete() {
+		/* Arrange. */
+		$sensei = Sensei();
+
+		/* Assert. */
+		$this->assertSame( 10, has_action( 'upgrader_process_complete', [ $sensei, 'maybe_initiate_rewrite_rules_flush_on_translation_update' ] ) );
+	}
+
+	public function testMaybeInitiateRewriteRulesFlushAfterLanguageChange_WhenLanguageChanged_UpdatesOption() {
+		/* Arrange. */
+		$sensei = Sensei();
+		update_option( 'sensei_flush_rewrite_rules', '0' );
+
+		/* Act. */
+		$sensei->maybe_initiate_rewrite_rules_flush_after_language_change( 'a', 'b' );
+
+		/* Assert. */
+		$this->assertSame( '1', get_option( 'sensei_flush_rewrite_rules' ) );
+	}
+
+	public function testMaybeInitiateRewriteRulesFlushAfterLanguageChange_WhenLanguageNotChanged_DoesntUpdateOption() {
+		/* Arrange. */
+		$sensei = Sensei();
+		update_option( 'sensei_flush_rewrite_rules', '0' );
+
+		/* Act. */
+		$sensei->maybe_initiate_rewrite_rules_flush_after_language_change( 'a', 'a' );
+
+		/* Assert. */
+		$this->assertSame( '0', get_option( 'sensei_flush_rewrite_rules' ) );
+	}
+
+	public function testMaybeInitiateRewriteRulesFlushOnTranslationUpdate_WhenNonTranslationUpdate_DoesntUpdateOption() {
+		/* Arrange. */
+		$sensei = Sensei();
+		update_option( 'sensei_flush_rewrite_rules', '0' );
+
+		/* Act. */
+		$sensei->maybe_initiate_rewrite_rules_flush_on_translation_update( new stdClass(), array( 'type' => 'a' ) );
+
+		/* Assert. */
+		$this->assertSame( '0', get_option( 'sensei_flush_rewrite_rules' ) );
+	}
+
+	public function testMaybeInitiateRewriteRulesFlushOnTranslationUpdate_WhenTranslationUpdate_UpdatesOption() {
+		/* Arrange. */
+		$sensei = Sensei();
+		update_option( 'sensei_flush_rewrite_rules', '0' );
+
+		/* Act. */
+		$sensei->maybe_initiate_rewrite_rules_flush_on_translation_update( new stdClass(), array( 'type' => 'translation' ) );
+
+		/* Assert. */
+		$this->assertSame( '1', get_option( 'sensei_flush_rewrite_rules' ) );
+	}
+
 	/**
 	 * Create courses and comments for the course.
 	 *