Minor refactoring of t().

framework/yii/YiiBase.php

@@ -606,10 +606,7 @@ class YiiBase
 	public static function t($category, $message, $params = array(), $language = null)
 	{
 		if (self::$app !== null) {
-			if ($language === null) {
-				$language = self::$app->language;
-			}
-			return self::$app->getI18N()->translate($category, $message, $language);
+			return self::$app->getI18N()->translate($category, $message, $params, $language ?: self::$app->language);
 		} else {
 			return is_array($params) ? strtr($message, $params) : $message;
 		}

framework/yii/i18n/I18N.php

@@ -78,16 +78,11 @@ class I18N extends Component
 	 * @param string $category the message category.
 	 * @param string $message the message to be translated.
 	 * @param array $params the parameters that will be used to replace the corresponding placeholders in the message.
-	 * @param string $language the language code (e.g. `en_US`, `en`). If this is null, the current
-	 * [[\yii\base\Application::language|application language]] will be used.
+	 * @param string $language the language code (e.g. `en_US`, `en`).
 	 * @return string the translated message.
 	 */
-	public function translate($category, $message, $params = array(), $language = null)
+	public function translate($category, $message, $params, $language)
 	{
-		if ($language === null) {
-			$language = Yii::$app->language;
-		}
-
 		$message = $this->getMessageSource($category)->translate($category, $message, $language);
 
 		if (!is_array($params)) {