Hi. I'm having this question.
I translated an add-on a few weeks ago and exported the phrases for the add-on. Now I want to upload it to my another installation of Xenforo but I can't figure it out how to do it.
Could you help me?
You'd just import it like any other language. Specifically, you'd import it on top of an existing language. A language that was exported for a specific add-on only replaces the phrases of that add-on.