Fix the issues reported by phpcs

The changes are fine. Maintainers should check if it is good to go or not.

The issue summary should always describe what the issue is trying to fix and, in the case, of coding standards issues, show which command has been used, which arguments have been used, and which report that command shown.

-    $language = (isset($message['language']) ? $message['language'] : language_default());
+    $language = $message['language'] ?? language_default();

The null coalescing operator requires PHP 7, but Drupal 7's minimum PHP version is lower. The current code is already corrected. The used rulesets are for Drupal 8 and higher, not Drupal 7.

Updated the issue summary with required details.

Changes are done to files contained in a branch, not a tag. The version I set is correct.

Also, another issue has been already created for the same purpose, two days ago.