Pot and kettle? :)
Yeah, the other part is about error messages and actions in progress, but let's focus on this one for now.
I chose the verbs "Otkaži" and "Odustani", both meaning "Cancel", in testing purposes. Just to let you know, "Otkaži" and "Odustani" are imperative forms (the first number in the brackets below, which shows how many results are there for that form), while "Otkaz" and "Odustajanje" are noun forms that Mihajlo uses.
Tausdata.org (13:0) — this one is actually Croatian, but they are using the imperative form in this purpose, too.
This means that there are no results AT ALL for the words in noun forms in the context of buttons. By the way, Google is using imperative too, of course. Just look at YouTube or Gmail.
P. S. Take a look at Serbian portal page.