Have you looked at Domino

Re: latency, unfortunately somewhat slower performance is to be expected here, since v1 used Firefox's native DOM parsing and the Node-based v2 uses JSDOM. We have some hacks in place to work around severe performance problems that JSDOM had on some pages, and they have some upcoming fixes that should fix that and hopefully speed things up in general.

We've implemented Accept-Language forwarding upstream.

We've added support for this in translation-server:

Not sure what you're planning, but the initial version of our Node port is up:

We've gotten translation internals working in Node. We'll be hooking those up to the existing translation-server endpoints and should have a working Node server that you can use within a few weeks.

Just a quick update from our end.

there are currently two deadlines here:

Firefox 52 ESR (which this is indirectly based on) EOLs in August 2018

Zotero dev here. I'm not clear on when all the above was written, but a few clarifications.