Google Trends can provide a possible first indicator of whether a term (name) is used in a particular language. However, the result should not be regarded as the absolute and only truth, but only as a strong indication.
If an exonym is no longer used but can be historically proven, it should rather be found in old_name=*. If the exonym is still used, then it should be in name:xy=, in this case name:de. It is also in ‘use’ - completely independent of Google Trends - also when it appears on local signs.
Translated with DeepL.com (free version)