...Is it common for english speaking countries to use "ac" as short form for "account"? ...
As you may have concluded by now, there is no single answer for all English-speaking countries - just as there is no single answer to many other language questions for all English-speaking countries. The short form
ac for
account is not used in U.S. English (American English, AE). As
Copyright posted, we use
acct. Others have said that it is used, perhaps with a slash in the middle as
a/c, in British English (BE). You may get different answers from Canadians, Australians, and so on (though I don't know how many different answers there can be to a question that must be answered by "yes" or "no," after both of those have been said).
P.S. The word "English" is always written with an initial capital E.