I'm probably not the best person to answer this, as I hate even reading things that aren't complete, let alone translate them. (This might be why I mostly stick to classics these days.) Can't say I've never translated a work in progress, but Yotsuba&! is a special case as it's not exactly a story where the plot matters, or even exists.

I will say, as a translator, I would be extremely uncomfortable translating a novel I haven't read to the end. So many things can happen, later on, that change your interpretation of earlier scenes, passages, sentences -- in ways that affect how you render them. I'd be even more uncomfortable letting anyone else see it till I finished and had a chance to revise through from the start.

(That said, I've been serializing early drafts of a translation of 道德经 even though I haven't gotten through it, willfully, but being explicit that pretty much everything is provisional till I have full context and can make final decisions. I'm not entirely consistent, no.)