Generally the three languages (four written, Bokmål and Nynorsk variants for Norwegian) are possible to be distinguished between, but there are also a lot of words that are the same (with same or different meanings) across the languages. The example was not much different than @vermillon’s
we could take example of the many words that are shared among European languages, I’ve provided “face” as a random example of word that exists in many languages
Either way, further discussion about the similarities (or not) between the Scandinavian languages are off-topic for this topic, so let’s move this to another topic if you want to discuss further.
I don’t see anyone saying this (ie., that is a strawman). A release with track titles clearly in English but lyrics in Russian should still have its language set to English.
However, in the case where the tracklist can be one (or more) of multiple languages based on how it’s written, either set it to the most specific one possible (in this case “Chinese”, in other cases could be unset/empty or maybe some other language). However, if listening to lyrics (or through some other investigative measure) it becomes clear that the language is a more specific one, then it should be fine to set it to that.
If it’s a release of erhu instrumentals, there will obviously be no lyrics, and thus the release language will not be able to be determined by lyrics and you’ll have either take the tracklist at face value (Chinese) or investigate more (e.g., ask the artist). On that same note, I wouldn’t take place of publication(/release) to mean anything for release language. If a Taiwanese artist makes a release in Mandarin Chinese by artist intent (but indistinguishable from Cantonese) and it’s re‐released in Hong Kong, I’d say the artist intent is still that the release is in Mandarin.