Wordless thoughts on the matter:
Challenging question. I would say that in this case, there is little interacting dialogue between characters (they don't speak the same language), so you might want to just go with any direct word-for-word thought-quotes in Italics, while if you describe what someone is thinking, it's in regular script. But people rarely think in "I" terms in their head. Most thoughts are conceptual and don't turn into words as such. I've asked a Russian co-worker (while thinking about this concept) if they think in English, and they said it sometimes happened, but generally their thoughts are not in words.
As she wandered through the room, she wondered what the strange devices were for. She held a round device and a memory began to surface of a class she once took. This is a force field generator. She set it down, awed by the possibility.
Generally, however, I have lots of interaction between characters talking, and really like describing their thoughts, as this is a good way to define who is talking other than saying he said/she said/John said. This pert is less critical in your story, so I think italicizing "worded" thoughts separately might work in your case.