Background specific languages are definitely, extremely silly. That said it's hard to know to what degree they are intended (and will be interpreted) as the suggested backgrounds, or the backgrounds, versus just examples of the sort of background players could make. The all adventurers are trilingual at a minimum idea is also silly.
The system is more modular than ever in principle. I like that on the customizeability front.
I think there should be a default, fits any background feat (my suggestion elsewhere was expertise in your two background skills), with subbing it out for a different level 1 feat presented as an advanced option. Feats are great, but it's a whole additional system with major opportunity costs that new players have to wrap their minds around to build a custom background and I think it can be simpler than that.
I am curious if traits, bonds, ideals, and flaws are going the way of the dodo. On the one hand they are a barrier to creating custom backgrounds and I rarely used them myself. On the other hand some players, particularly those new to roleplaying, definitely found them an inspiration. They were also a lot of what potentially gave the thematics of background actual weight on a character.
I do kind of feel like if everything about a background is completely modular and custom what is the point of putting it all in a package and calling it a background rather than just giving people a list of additional things beyond race and class to choose. Particularly this seems silly in terms of the choose a "background then choose a language" presentation. Why not just have every background tell you to choose two languages?
So I guess on the one hand I like backgrounds being more modular, but on the other hand completely modular backgrounds cease to be a coherent thing beyond the will of people to make character building decisions based around being true to whatever background they dream up.