Agree with this.
I always have seen them as songs with no lyrics. But MB taught me that it is not a song unless it has words to sing. Which is confusing as what does the song writer get paid for on his\her invoice when they write music without words?
If people insist that a “Song” requires words and intent to be performed by a voice, despite modern usage of the word “song” not requiring voices or words in many circles, then we definitely need a new work type to cover instrumental music, with the emphasis on “Music”.
After all, I count 5 existing Work types which aren’t themselves a piece of “Music” that you would have a recording of:
I don’t agree that setting the lyrics language to “no lyrics” is enough.
when speaking of corner cases, don’t forget about whistled languages. If it sounds like somebody just whistling, in fact he may be singing “Ave Maria” in whistled language 
Where would Mongolian throat singing fit? Well I generally use, World, Folk.
As for non classical works without lyrics, I’ve always just used “Instrumental” for pieces from Percy Faith, Mantovani, etc. Some songs without lyrics like Glenn Miller could be tagged as “Swing” or “Big Band”.
Are works like Tubular Bells, Pop or Instrumental?
When you get into areas like “swing” or “big band” you’re really talking about arrangements and performances, not the work itself, and that’s a different topic.
Keeping to the original question, I think an “instrumental” work type could be useful, with a couple of caveats:
Not sure if anyone cares anymore, but at least one editor has taken it upon themselves to change all video game-related works into Songs, despite being advised that it is ill-advised.
https://musicbrainz.org/edit/82169710
https://musicbrainz.org/edit/82283184
I think it’s a pity that, because in English the word song apparently includes instrumental wrongly, the MB Song work type then includes instrumentals.
Then for me, this work type (Song) has no longer much meaning or purpose.
Maybe it’s only a Classical type, like the other types, after all.
I will continue to use song only for vocal works with lyrics and no type for instrumentals but there is no guideline preventing other editors to break/change this afterwards.
This argument pops up again every few months due to the confused definition in English. Like in many areas, MB diverges from standard English with its own terms. Newbie editors often will not have seen the previous discussions and maybe it needs some better clarity on the guideline wording. It would be simple to solve with an “instrumental” type, but that is lost in a ticket somewhere.
It always seems odd to me that we have to leave a space as that just reads like “undefined” to me.
When I look up anything related to works on a soundtrack, they are called “songs” by everyone. I find “song” to be the most appropriate of the given types for these works. Until a “more correct” work type is introduced, “song” remains the “most correct” of the given choices of work types, and certainly better than a blank field.
That’s… highly debatable. I personally consider a blank field a lot better than “song”
It should be noted that the style guidelines don’t say anything about what Musicbrainz officially considers as the definition of “song”.
Maybe it’s time to correct that.
Our current definition of “Song”, as seen when selecting the type in the work edit page, says:
A song is in its origin (and still in most cases) a composition for voice, with or without instruments, performed by singing. This is the most common form by far in folk and popular music, but also fairly common in a classical context (“art songs”).
This suggests that it is meant for voice, but it doesn’t explicitly limit its use for non-vocal music because of the whole mess which is the English language. I’d be happy to limit it further, if there’s anywhere approaching community consensus about it, but I remember this being fairly controversial in the past.
Huh… I almost said in my previous message “nowhere in Musicbrainz docs…”
I feel like it’s a bad thing for the only documentation of a particular (sub-)rule to be in the context-documentation of the edit page.
And/however, I agree that the wording there (the context-doc) is not very “rule”-ish.
This topic shows that it’s eventually not everyone, who would say song for instrumental.
And actually, if you see this text when editing:
Could you please revert your song edits?
Shouldn’t soundtracks (be it for film, television or video games) be set to the work type of Soundtrack ?
" A soundtrack is the music that accompanies a film, TV program, videogame, or even book. "
The soundtrack itself should, but each piece inside a soundtrack is not itself a soundtrack, in the same way that each track inside an album is not itself an album
Just my 2 cents here - should production music have a separate category or it already falls into some existing one?
Do you mean music produced for use in things like broadcast television or the royalty free libraries used for things like YouTube?
At the moment, so long as it has no lyrical content you want to use - Type [blank], Lyric Language [None]
If it has lyrics then it should be - Type [Song], Lyric Language [the language of the lyrics]