Before you start: test every pattern with examples that should match and examples that should fail.
ASCII letters only
This pattern restricts the entire value to A-Z or a-z.
Regex: ^[A-Za-z]+$
Adding common accented letters
Manual ranges can expand coverage, but they are easy to get wrong or incomplete.
Regex: ^[A-Za-zÀ-ÖØ-öø-ÿ]+$
Unicode properties
Modern engines may support Unicode properties such as \p{L} for any letter, usually together with a Unicode flag. Check your language support.
Do not over-restrict real names
Human names may contain spaces, hyphens, apostrophes, and characters from many writing systems. A simple “letters only” exercise should not become a harmful production validation rule.
Next step: test it for real
Use the Playground to experiment with the pattern, then practice in the game with feedback on false positives and false negatives.