It looks like this game uses Oodle for file compression (there is oo2core_4_win64.dll in What Remains of Edith Finch\Engine\Binaries\ThirdParty\oodle\Win64 folder).
I don't know how to decompress them (after extraction from .pak, nor during extraction with UE4.bms).
Here are some extracted files from main .pak archive:
Yes it's oodle (confirmed in my raw tests here) but I think there is something missing. First of all your files have lot of zeroes and then I don't know what should be the exact decompressed size of these files because oodle may be a bit "picky" about it.
I'd really like to translate the game to my native language with my pals. Can anybody give me a quick rundown how can I make it happen? I'm pretty new here