The term you are looking for is 'creole' or 'pidgin' (which are often used interchangeably). From my field of study, perhaps West African Pidgin English? It was used in the late 17th and 18th centuries and was used by West Africans with what they picked up from Europeans during the Atlantic slave trade.
It took most syntax and grammar from substrate languages (mainly those from West Africa), but the vocabulary was mainly from the superstrate English, here's an example:
“Me? Put poison for master? Nevertheless!” said the cook, side-stepping to avoid a heavy blow from the Minister. . . . Why I go kill my master? . . . Abi my head no correct? And even if to say I de craze why I no go go jump for inside lagoon instead to kill my master?" (a servant, in [Chinua] Achebe's A Man of the People, p. 39)
But anyway, as others have said, any creole or pidgin would be what you are looking for. Pidginization is when two languages literally clash, and speakers are forced to pick up words from each other over time in order to accommodate each other. Think of a plane full of Chinese speakers and English speakers crashing on an island. Assuming there was no domineering or anything, they would each over time pick up parts of each other's language, and slowly develop a language that was a combination, which we call a pidgin. An example known to you could be the simplified English you may speak to a foreign waiter while abroad. Creolization occurs when the descendants of these people speak the pidgin language as their primary tongue, and we now call it a creole.
Sadly in reality we often have socio-economic issues which cause one language to be more dominate (superstrate/substrate), so its kind of hard, maybe impossible to find an example where the language is 50/50 mixed.