It’s baffling to me that she doesn’t want a connection with her own FIL and yet will complain at being excluded.

Who says she doesn't want a connection to her FIL? There's a difference between having a connection to someone and learning a whole new language. She also said she would try, maybe OOP should give her more than two weeks before he decides to ruin his marriage over it?

But it’s also OOPs right to feel unsettled by it and perhaps, realize this marriage isn’t for him - especially if he wants children in which ASL will be absolutely necessary.

Yeah that's his right, but maybe he should have communicated this shit BEFORE he got married, and BEFORE it became an ultimatum, within the space of two weeks, to maintain their marriage? Especially if it involved ADOPTING A HUMAN BEING.

Sounds like we as readers can see their marriage isn’t meant to be, but now they have to realize that on their own.

It sounds like you're biased as fuck and you haven't considered the wife's side of this at all.