What may look like decoration to English readers e.g. the ä in häagen dasz or ö in Motörhead, are actually distinct letters in languages that have them. Disallo

What may look like decoration to English readers e.g. the ä in häagen dasz or ö in Motörhead, are actually distinct letters in languages that have them. Disallowing display names because another one exists but without diacritics and the like is just asking for a ton of manual review. And how do you handle scripts that only use ASCII for English loan words, say Chinese, Japanese, Thai, Arabic, Russian and Indian scripts?