code: protected function loadMessagesFromFile($messageFile, $category)
      {
          if (is_file($messageFile)) {
              if ($this->useMoFile) {
                  $gettextFile = new GettextMoFile(['useBigEndian' => $this->useBigEndian]);
              } else {
                  $gettextFile = new GettextPoFile();
              }
              $messages = $gettextFile->load($messageFile, $category);
              if (!is_array($messages)) {
                  $messages = [];
              }
  
              return $messages;
          }
  
          return null;
      }
docs: Loads the message translation for the specified language and category or returns null if file doesn't exist.
  
  @param string $messageFile path to message file
  @param string $category the message category
  @return array|null array of messages or null if file not found