Regular expressions - the horrors of validation

I got up a simple task - to make a registration form and check it for correct input. But my boss is pedantic and constantly inventing such tests that validate my work :-) I successfully overcame my phone, email, etc. And now the worst thing is checking the name and surname. A simple rule like ^ [a-zA-Z '' - '\ s] $ he absolutely does not like - we still need letters with umlauts and other tails, several types of apostrophes ... I was completely tortured! I am the only programmer in the company and I immediately deal with 2 sites - I support the old one and write a new one in the breaks ... I will be glad for any help.