you want it for interlude, well interlude miss instances, therefor u are forced to accept parties one by one keep that in mind.
1) you can use Dimensional Rift it does excactly the same thing, you can mod it tho.
3) I cant understand
4) Your request is bad, the gameserver isn't intelligent in order to find the translations by itself, I dont think that you can connect it with some kind of DataBase with all the translations but if you can't you will have to do it static way (xml) or HTML, but still, its impossible (lots of work, critical RAM consumption with low results) But: For a few HTMLs you can do it by ur own, to translate them in different languages and then depending on the language of the user show the coresponding HTML. Nothing unique for this