I need to match any letters (like MS Office Word find with special character ^$ functionality) with regex.
I've tried with `[a-zA-Z]` but don't match any unicode letters like accent letters or ä, ö, ü, ß. 
I've tried also with `[a-zA-ZäöüßÄÖÜ]`but there are too many letters. 
Is there any regex to match all this letters?