I liked the bfavaretto solution more, but I'll leave a shorter alternative here:
var reg = /[a-zA-Z\u00C0-\u00FF ]+/i
Explanation: this is a match of the characters 'a' through 'z', 'A' through 'Z', and finally, all Unicode characters from 'À' to 'ÿ', so I think should include all accented characters.
The full list of Latin characters in Unicode can be seen here: link
The complete list contains about 128 characters, of which only one part is used. The expression I used includes some strange and unlikely ones, like the Æ and at least two mathematical signs. You may want to use a more accurate expression such as bfavaretto, or use narrower Unicode strings.