>"I was in 東京 yesterday"

I think it's the wrong example, because this is actually very common if you're a Chinese speaker.

Actually, people tend to say the name of the cities in their own countries in their native language.

> I went to Nantes [0], to eat some kouign-amann [1].

As a French, both [0] and [1] will be spoken the French way on the fly in the sentence, while the other words are in English. Switching happens without any pause whatsoever (because there is really only one single way to pronounce those names in my mind, no thinking required).

Note that with Speech Recognition, it is fairly common to have models understanding language switches within a sentence like with Parakeet.