I dicovered that the edit summary used in the add a link feature is in the user's language, not content's language, which means that if a cswiki user has the interface in Arabic, the edit summary will be in Arabic, rather than (expected) Czech.
Should be easy to fix :).
Screencast: https://drive.google.com/file/d/1DML7fs1Fr8bM3s3Kmn8Jc3I91G-hBgTL/view?usp=sharing