The role of the Biritish Prime Minister is similar to that of German Chancellor (i.e. the head of government) but not identical.
Normally it’s not translated, so Mrs. Merkel is referred to in Britain as the German Chancellor (not German Prime Minister). Similarly, I believe David Cameron is called the Premierminister in Germany.
In Britain, the Finance Minister is called the 'Chancellor of the Exchequer', often shortened to just 'Chancellor'.
How charmed I am when I overhear a German word which I understand! - Mark Twain