Reading up on Novegradian, I see that my confusion about the lateral consonants was due to unfamiliarty with IPA, and it's a contrast between clear L and dark L. Both exist in English, except not quite, because English has alveolar L, and Novegradian (and apparently also Russian; I am learning so much Russian phonology, and getting progressively more annoyed with how evidently inadequate Duolingo is on its own) has dental L.
Okay, I say all that, because that's what Wikipedia says, but I can't tell the difference audibly, and also, I'm pretty sure I actually use both in English? Like, alveolar for word-final L, and dental otherwise. (Except that's not quite right, because "lull" is all alveolar, "lily" is all dental, and the second L in "little" remains alveolar even if I add a suffix. I think compound words count as "not word-final". "Small" is alveolar, and I think "small-minded" is dental.) Is that a thing?
Well, my wife got similar results, and neither of us can tell what's going on by listening. I should stop messing with this for now, because now my tongue is a little sore.
Anyway, yeah, a bit more progress reading about Novegradian, and a bunch of learning about natlangs.