Nominatim currently has a problem with searches where the words have many transliterations into different languages. It basically ends up with too many variants to search to and gives up before hitting the right one. In your example is it tripped up by the many “translations” of Unter den Linden which are all simple transliterations. (The English version really makes me cringe. Does anyone ever use that?)
Anyway, just saying that Nominatim is simply buggy here. It should find the hotel under both search terms. Fix is planned but will need another month or two. If you want to track it, follow 2 Ulmenweg, Hildesheim not found · Issue #2855 · osm-search/Nominatim · GitHub