With regards to in-game, I could certainly see pilots speaking a non-English “mother tongue”, but then studying English or another commonly-known language for GTA service, especially if a particular planet or colony's settlers had a certain heritage. All the pilots, i imagine, spoke English simply because it was a US-made game and targeted primarily on the US/UK audience , which is used to western-ish sci-fi cultures, and they could only afford to really grab western voice actors. Had it been made in Dubai or Beijing, then their languages would’ve been the major one.
If your mod project does has the opportunity to bring in foreign language speakers, then I encourage you to go for it and have the translator as you say; having wingman with accents and sometimes slipping into their mother tongue when muttering, swearing or panicking would be awesome, and would really bring to life projects where cultures are dominant (such as TVWP, whose ships had very Russian-sounding wing names, so I assumed the PRM to be quite Russian). I also genuinely like to see other cultures in media; I hate seeing nothing but English-speaking Caucasians or westernised people! Variety is the spice of life.
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English at the moment is likely quite common as a second language because of the British Empire colonising everywhere (been reading a book all about it recently in fact called "
Orientalism" by Edward Said, scary book
). We Brits were a bit big-headed back then and essentially went around forcing our ways on other cultures, hence the prevalence of English in business; it or dialects of it (American English etc) are known to a lot of people, and the US’s worldwide presence with their version of English has kept it alive.
As Iranon said, it does change across history depending on the nation in dominance; in the Middle Ages French was "the language of the educated European", and I imagine Latin was before that. I've heard that Spanish is slowly overtaking English in some areas, but in the future i wouldn't be surprised if Chinese and/or Arabic become major languages (especially the latter; my impression is that virtually all of Arabia speak Arabic or a closely resembling language).
