My friend is working on Grammatical Framework, which has a Resource Grammar library of pre-written natural language grammars, at least for portions of them. The GF research community continues to add new ones over time, based on implementing portions of written reference grammars, or sometimes by native speakers based on their own native speaker intuitions. I'm not sure if there are larger grammar libraries elsewhere.

There could be companies that made much better rule-based MT but kept the details as trade secrets. For example, I think Google Translate was rule-based for "a long time" (I don't remember until what year, although it was pretty apparent to users and researchers when it switched, and indeed I think some Google researchers even spoke publicly about it). They had made a lot of investment (very far beyond something like a GF resource grammar) but I don't think they ever published any of that underlying work even when they discontinued that version of the product.

So basically there may be this gap where academic stuff is advancing slowly and yet now represents the majority of examples in the field because companies are so unlikely to have ongoing rule-based projects as part of projects. The available state of the art you can actually interact with may have gone backwards in recent years as a result!

nimi sina li pona tawa mi.