How to only allow alphabets and spaces in the middle in Profile2 field
I've found the Field validation module that works! I used this regex expression:
^[\x{00c0}-\x{01ff}a-zA-Z0-9]+([- '][\x{00c0}-\x{01ff}a-zA-Z0-9]+)*$

This way I can allow international names and only allow spaces, hyphens and apostrophes in the middle of the name.
It was based on combining

1 https://stackoverflow.com/questions/275160/regex-for-names , and 
2 https://stackoverflow.com/questions/2525327/regex-for-a-za-z0-9-with-dashes-allowed-in-between-but-not-at-the-start-or-e