Write what people intended to say, not the sounds of the words.
We don't write character accents phonetically (hopefully). We don't add every "um…" and pause that's used in normal speech. Instead we write what characters meant, not the individual phonems coming out of their mouths.
By extension, we don't need to hear that lizardmen lisp the letter S, and that werewolves have trouble with P and M because fangs don't allow their lips to close. Unless there is some specific comedy of errors because of a mispronunciation, or the accent makes them the butt of a joke, it's better to just write what they meant.
Speaking a different language is a bit of a leap, but really it is the same idea. It doesn't matter which language they use at any moment, they may be bilingual or working among others in a common language of borrowed words, what matters is what they intended to communicate. So just write what they meant.
When the POV is third-person limited, your MC will either understand what was said or not, as the plot dictates. The longer she hears a foreign language the more words she'll pick up, and the meaning will start to come across before she becomes a fluent speaker. You can show this by having her understand only a few words at first: "Stephanie… airlock… come!" It's not that someone is speaking to her in a pigeon language, it's that she is only picking up familiar words.
Characters in a bilingual environment will share words from both languages mid-sentence, and fluent speakers will be comfortable speaking in both languages, so consider it a skillset among your characters rather than a realworld detail you need to show the audience.