polyglot

'[T]is thought the two and twenty Languages which Mythrydates the great Polyglot King of Pontus did ſpeak, wer all within the circumference of Anatolia in regard his dominions extended but a little further: […]

a polyglot bible    a polyglot lexicon

A polyglot region without a clearly dominant culture may develop an artificial lingua franca, such as Pidgin English in the South Sea.