[Varyon]

In GURPS, I'd probably have characters rely on gestures, with rolls against the Gesture skill (or its IQ-based default) to get messages across. Note those you don't share a language with are also rather unlikely to share your culture, so Cultural Familiarity penalties are going to be in force. Vocalizations will undoubtedly be involved, so characters may eventually start to pick up smatterings of the others' language, perhaps enough for the two groups to develop a pidgin (which is probably a language that can't be purchased above Broken, but that the GM would be justified in letting characters purchase at a reduced cost - either in place of a skill in the Dabbler Perk or simply acquiring the necessary [1] with fewer hours of study).

Tangentially, I'm now tempted to try and design a character who, unbeknownst to him, has a psionic ability to be understood at the Broken level, so long as he speaks his native tongue clearly and loudly. Said ability would, naturally, be called GOLE - Good Old Loud English (I think that's the term I've seen used, but for some reason Google gives me no relevant hits). He may have a Delusion that everyone can understand Good Old Loud English to some degree.