I never really understood the insistence on diacritics. My name is properly written in Hebrew characters, and contains sounds not present in the English language. Many more people use CJK, Cyrillic, Arabic, or other characters. The writing system in use by many people and companies for the English language does not support any of these characters, and nor does it support diacritics. Some variants (in particular, see airlines) use only capital letters, with no spaces or dashes; this also seems reasonable to me (even when my name is somewhat mangled as a result). So just like a CJK/Cyrillic/Semitic name has to be roughly transliterated into Latin characters, and inevitably pronounced differently than in its origin language, why shouldn't the same be true for names with diacritics? Saying that the One True International Alphabet is latin-1 or whatever is rather arbitrary. And no, the solution isn't to give up on cross-cultural communication, nor to require that every human learn all the characters in Unicode.
A Belgian bank requiring a Belgian person to transliterate their Belgian name to English characters is somewhat similar to an Israel bank requiring to transliterate your name from Hebrew to Korean (which has as much relevance to Israel as English has for Belgium), and refusing to use Hebrew in their communication.
There are official national languages and alphabets, the involved characters are key parts of those national alphabets - who cares about what the English alphabet is? Neither the bank nor the customer are in England or in an English-speaking country, and there is a legal duty for the bank to support the national language(s).
You're right, I was thinking of this in the context of an English-speaking country/institution (mostly since I do often see this demand in those contexts as well; to be clear, I think it's a reasonable request, but not a reasonable demand or legal requirement). In the context of a Belgian customer of a Belgian bank it's definitely more surprising; but I also wouldn't categorize it as "inaccurate personal information", but awkward transliteration to a foreign alphabet; as you said, that may be strange and possibly even run afoul of national language laws, but I wouldn't use GDPR against it
> [Korean] has as much relevance in Israel as English has in Belgium
Legally maybe, but certainly not demographically/culturally; I mean, certainly there is a difference in the expected probability of being understood, especially given the highly-overlapping character sets
