Zompist Bboard Again

Let's say in an isolated place you mix a thousand people 500 of whom speak only Russian and 500 speak only Japanese.

Do you think that emergence of a mixed language with grammatical features from both languages is a possibility?.

I am asking because if there are only two ancestral languages, then even if the first generation develops a simple Creole to communicate, the next One will be fluent in that creole AND languages of their parents. It will be much easier tomix varius grammatical features

It's possible, but it's also possible for the next generation to learn both languages fluently. (After all, people learn languages fluently by immersion all the time.) There would probably still be some language mixing but it could be garden-variety codeswitching rather than a true mixed language.

I recommend Thomason & Kaufman's Language Contact, Creolization, and Genetic Linguistics here. They review all sorts of contact situations.

There is such a thing as a "mixed language", as T&K call it. An example is Michif, spoken in Canada. In general, the nouns are from French and the verbs from Cree-- in both cases following the morphology of the source language. Articles and adjectives are French, demonstratives are Cree; and these elements follow both French gender (masculine/feminine) and Cree gender (animate/inanimate).

Things to know about mixed languages, though:
1. They're very rare. T&K find just 6, IIRC, while there are dozens of creoles.
2. They don't develop from creoles. Creoles develop on their own terms, or they may be partially decreolized by borrowing from the source language.
3. They develop among populations that are bilingual. The complicated mixed morphology of Michif is not a compromise; it could be mastered only by people who knew both languages.

From a conworlding point of view-- or a linguistic one-- what happens in language contact does not depend at all on the nature of the languages involved, but on their sociolinguistic relationship. Which has more speakers? Who is dominant? Which is spoken by whom, and under what conditions? How much do the language communities have to interact?