I couldn't find a topic about this, so my apologies if it's already been suggested.

I can use tags for this, but basically I like to know which languages are available and which languages I've played. (Also related but less likely to be of general interest: input method.) It's especially the available languages where a centralized DB would come into its own.

I completed Tomb Raider (2013) twice in English on Windows, once with mouse and keyboard, a few years later with an Xbox One controller, and a few years later once more in French on Linux. If I ever play Unforeseen Incidents again, naturally I’ll do it in German.

To properly make use of that I’d also have to track which languages are supported by a game, so that I can do something like filter a list of games that I last played through at least four years ago, that I haven’t played in French yet.

That’s not some convoluted invention on my part. It’s pretty much the only scenario in which I’d consider replaying a game like Monkey Island right now. On sites like GOG and Steam it's easy to search for games available in a particular language, so I'd say it's pretty standard. ;)

Edit: also, I just noticed you can't seem to search for "doesn't have tag X"?