I realize that the error rate would be a lot higher if Siri also has to determine in which language you are speaking. So maybe one solution would be to select two languages in settings, one "command language" (open, search for, call, ...) and an "alternative input language", so if you e.g. say "call (name pronounced in German)", Siri will determine whether the name you say is German or English and use the respective algorithm. It's kind of like the separate setting for Language and Region Format - and highly appropriate in a world where many people are multilingual in their every day lives. Eitherway, they should definitely add a feature that allows you to have Siri pronounce street names in the language of the respective country in turn-by-turn-navigation. That is easy to implement.
