regular expression for French characters

Try:

/^[\p{L}-. ]*$/u

This says:

^         Start of the string
[ ... ]*  Zero or more of the following:
  \p{L}     Unicode letter characters
  -         dashes
  .         periods
            spaces
$         End of the string
/u        Enable Unicode mode in PHP

/^[a-zàâçéèêëîïôûùüÿñæœ .-]*$/i

Use of /i for case-insensitivity to make things simpler. If you don't want to allow empty strings, change * to +.

The character class I've been using is the following:

[\wÀ-Üà-øoù-ÿŒœ]. This covers a slightly larger character set than only French, but excludes a large portion of Eastern European and Scandinavian diacriticals and letters that are not relevant to French. I find this a decent compromise between brevity and exclusivity.

To match/validate complete sentences, I use this expression: [\w\s.,!?:;&#%’'"()«»À-Üà-øoù-ÿŒœ], which includes punctuation and French style quotation marks.

Simplified solution:

/^[a-zA-ZÀ-ÿ-. ]*$/

Explanation:

^ Start of the string [ ... ]* Zero or more of the following: a-z lowercase alphabets A-Z Uppercase alphabets À-ÿ Accepts lowercase and uppercase characters including letters with an umlaut - dashes . periods spaces $ End of the string