My current piece in 3rd person involves lots of internal dialogue because the character is somewhere they can't speak in the local language. I've been advised not ever to use 'I' in this perspective, even when expressing the person's thoughts. For example:
"Oh god," she thought, "why can’t I think straight?"
Another example:
"This is what I came here for," she thought.
What's the best practice in using 'I' in third person internal dialogue?
A close third person is effectively a first-person narrative with different grammar. In the case that you give, there's no reason not to write it as:
When was the last time she had more than a few hours’ sleep?
In a passage of close third person, it will be understood that the question is the protagonist’s thought and not the narrator’s interjection.
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 part is less critical in your story, so I think italicizing "worded" thoughts separately might work in your case.
