It could mean “national language”; that is, any language which is the official national language of some currently-existing national-state.
It could mean “native language”; that is, any living language which some living speakers acquired as their L1, and other future-speakers are currently in the process of acquiring as their L1s.
Or it could mean “natural language”, that is, any language which was
Some say there are between about 4000 and about 7000 currently living* natural languages; depending on how one counts them and how one decides whether two speech-communities speak different varieties of the same language, or instead speak different languages.
*(For these purposes I think a language which is no longer in use is a dead language, even if some of its speakers are still living: And, a language which is no longer being acquired as an L1 is a moribund or “dying” language.)
Of those 4000ish-7000ish languages, around about 2000 have been well-documented; or, at least “adequate reference grammars” for them have been published. (I don’t know what makes a reference grammar “adequate”. Must it include a sizable portion of the language’s lexicon ?)
….
Clearly, most natural languages are no longer living languages.
In particular they are no longer anyone’s native language.
And the vast majority (at least 90%-95%) of currently living native languages, have never been national languages.
And others are no longer national languages; and most never will be national languages.
….
How many of us, and who among us, has read or heard or seen a use of “natlang”, wherein the speaker or writer could have plausibly meant “national language” or “native language”, rather than “natural language”?