I want to validate first-name sent by user with Regex. I found multiple expressions for first-name, but I also want to add german characters like
à À è È é É ù Ù ì Ì ò Ò ñ Ñ
Your regular expression does not match the subject string.
It is not a good idea to restrict people's names too much, I suggest a rather generic regex:
This regex will match a string only consisting of 1 or more Unicode letters, diacritics, whitespaces, apostrophes or hyphens.
If you need more restrictive checks, like a whitespace may only appear inside the string and only if not consecutive, use grouping: