Check if character is letter in Delphi (Unicode)

Are there pre-defined charsets in Delphi, to check if a character is a letter? In Cocoa I use something like ``` if ([[NSCharacterSet whitespaceCharacterSet] characterIsMember:character]) ``` I know I can do in Delphi ``` if c in ['A'..'Z'] then ``` but will this cover foreign accentuated characters like Á, À, Ú, É, ....? What would be the most efficient way to check this in Delphi. I need to check if a string is fully composed with letters.