Nyanta was spying on them the whole time. It's possible that real life Shiroe once used Roe 2 on a raid or some quest with Nyanta, and so he knows who Roe 2 truly is.
I'm guessing Shiroe also had told him about Nureha's world-changing magic so Nyanta also knows who Dariella is.
That bit about the auto-translator was not even something that I would've considered as essential, but it would seem that a game like Elder Tale that had different servers and players all over the world had a crude translator thing built into the game. I would've assumed that each region/server's players would've spoken the same language so they wouldn't have need translators at all, and yet Mamare in his infinite wisdom saw the need to address this apparent language barrier, brilliant!
I'm guessing that mobile temple and that wyvern horde are related somehow. Nyanta's eyes are also open when they're usually closed, that's like a universal anime sign that serious stuff is about to go down
