Just like instruments, I think it would make sense to have languages as entities instead of attributes.

1. Languages can have different names, not just in different languages, but also in the same language. For example, the language West Frisian is officially known as Westerlauwers Fries in Dutch, but everyone just calls it Fries, although that really is the name of the language family. An entity with aliases would make searching for either name a possibility. It would also make it possible to search for a language in a different language: A Japanese user with a French release in hand with track titles written in "Frison occidental" would be able to find the right language for his release.

2. Different languages can share the same name, but that can be solved with disambiguation comments.

3. ISO-codes could be implemented as attributes.

4. Languages are often grouped in families, but our current system doesn't list that information, and I think that would be way out of scope for MusicBrainz anyway, so I would suggest not implementing relationships between languages. Let's keep things simple and avoid LanguageBrainz.

5. Instrument-URL relationships could be established, like for Wikidata and Ethnologue.

6. It would be easier to get lists of releases, works etc. in a certain language, because that would be displayed on the language page. I think this would be interesting to have this information in a more accessible format.