What happens when people in a place speak several different languages?
Well, nowadays people might well all be able to speak English to each other, but there are other ways of solving the problem.
One is to take one of the languages, probably the language of the dominant group (though not necessarily the biggest group in terms of numbers) and use bits of vocabulary from the other languages stuck into some approximation of that. Quite soon you end up with a rather awkward means of communication called a pidgin - and then later, with a new generation of speakers, it will blossom into a new and supple language called a Creole.
The lexifer is the base language that has all the new vocabulary (and probably some grammar, too) inserted into it.
You can sometimes tell how far along this process has gone, and the what the lexifer is, by the name of the language. Malay Creole Portuguese tells you, firstly the place it's spoken (Malaysia); and then that it's developed into a proper language, a creole; and, lastly, that the lexifer is Portuguese.
French Guianese Creole has a French lexifer and it's spoken in French Guiana - though as far as I can see there's nothing (except history) to tell you it isn't the other way round.
Singapore English is usually called Singlish, which isn't easy, either.
Still, lexifer is a brilliant word for Scrabble, anyway...
...or it would be, if it was a valid word. Which it's not.
Word To Use Today: lexifer. The Latin word lexicon means vocabulary list.