What do you think about ignoring other language’s diacritics, umlauts etc.?

I’ve just written an answer about Pāṇini. I know what a macron is, and I know what a retroflex nasal is. I also know that the Sanskrit grammarian is not to be confused with an Italian sandwich.

Nevertheless, in my answer I referred to him as Panini. And I do not feel guilty for doing so.

Diacritics for other languages are appropriate in scholarly writing, and when you are writing for a bilingual audience, which will wince to see them missing. In a more casual context, on the other hand, it does come across in English as pretentious.

There is also a long standing convention that we are not as fastidious about diacritics on proper names. Proper names are embedded in otherwise purely English text. There is a strong driver to nativise them orthographically, since they are effectively used as part of English. The same goes for loan words. I pronounce jalapeno with a velar fricative and palatal nasal, because I’m pretentious like that, but I would still hesitate to use a tilde.

Language is full of contradictory pressures, and this is yet another instance: assimilation versus fidelity, nativisation vs exoticisation. The pendulum swings, as a matter of fashion, but the drivers behind each are legitimate. Dropping the tilde in a loanword is not disrespect to Spanish: it demonstrates how thorough the influence of Spanish has been in English, to have produced a nativised loanword.