Both ESO and SWTOR have fully voiced NPCs, but both games have budgets that were massively inflated for that purpose, and have trouble adding new story content due to requiring additional voice acting. They wouldn't be able to simply drop in new side quests each patch, without going to the trouble of hiring and directing more voice talent.

Then you have the issue of "is this actor still available?", "can we still use a character from 3 years ago?", "is it acceptable to hire a new voice actor for this character?". With ESO, it is teased that a character voiced by John Cleese will have a larger role in the future, but I don't see the game having a large enough budget expansion to validate hiring John Cleese to do more voice work. If they hadn't gone with voice acting, that character could tap dance his way through every story beat with no extra budget required.

Think of how we can revisit locations like Revenant's Toll or Camp Dragonhead, and various npcs will all comment on our current position in the story. Would they still be able to put those touches into the script if everything had a voice?

And yeah, there are four languages they'd have to do, so multiply these problems by four.