Change the language of a button
Usually when one speak about language change, she/he speaks about localisation change. That can be controlled from the localization in Admin Menu, and depends on whether you have a license for such language.
But when you speak about button, do you speak about Archer buttons like NEW/SAVE or about Advanced Workflow Buttons? Can you please clarify more and possibly provide screenshot?
This has to be changed in Advanced Workflow Modeler, you are speaking about Transition names (Arrows).
These are not subjects for localisation today, AFAIK.