" We already have street signs with Arabic and Japanese characters"
No, we don’t. Look at your own link. I see a standard street signpost that conforms to the law (official texts in Germany have latin characters mandatory, with the only inclusion of umlauts and the ligature of s and z). In your link, you see an additional label, which is just a service like those labels that explain e.g. who a certain celebrity was, whose name that street bears.
“and Cyrillic characters will also be installed at some point. Therefore, such a filter rule makes no sense, especially not in an international project.”
IMHO Wrong. There is one official street name, and this what has to be displayed. There are no non-latin characters in Germany. As a service, OSM could offer transliteration (not to be confused with translation), but this is highly problematic. In the case of cyrillic, there just is no letter “H” in cyrillic. Does not exist, and nothing to take it’s place phonetically. In the official russian transliteration rules, H shall be substitued by the cyrillic letter for G, which of course leads into loads of problems, disambiguities and misunderstandigs… Therefore, the official transliteration of the German city Hannover ist Gannover… (official meaning: According to official russian transliteration rules. By German law, Hannover is only Hannover.