[otrs] which changes are allowed in the "$Language.pm" file ?

Hi all, could I ask you to explain what kind of changes can be done in a language file ? Is it allowed to move lines (change order of lines) ? If I add a line somewhere, will it cause a problem ? If I do 50 changes in the file, how to note them ? Our sk_SK.pm file (used under 2.3.4) does not work under 2.4.1 version probably because of changes done in it. I appreciate your help. Thanks. Sincerely, Tibor.