Based on OP's comment history, he's Belgian or lives in Belgium. Seems that there's no such requirement in Belgium (https://be.brussels/en/identity-nationality/

Based on OP's comment history, he's Belgian or lives in Belgium. Seems that there's no such requirement in Belgium (https://be.brussels/en/identity-nationality/children/birth-formalities https://be.brussels/en/identity-nationality/children/birth-f...) and in many countries I know that ü is explicitly allowed. Potentially OP is talking about a set of requirements he imposed on himself? Edit: or maybe France? Either way, it's free choice still theoretically. https://en.wikipedia.org/wiki/Naming_law#:~:text=Since%201993%20the%20choice%20has,Napoleon%20Bonaparte%20created%20the%20law https://en.wikipedia.org/wiki/Naming_law#:~:text=Since%20199....