In last month's column, I wrote about the presence of Spanish in Omaha, attested by its occasional appearances in the broader English-speaking market. I also mentioned the phenomenon of people speaking two or more languages, called bilingualism. When a person has command of two languages, then that person is considered bilingual.
Considering that one language (like Swahili) might be called a code, and another language (Arabic) is another code, and a third language (like English) is another code, then conceivably a person who lives in Tanzania might carry on a conversation with another speaker from Tanzania in three different languages all in one conversation. This is called codeswitching. Often, people who can communicate with others who arc multilingual in the same languages will blend those languages together in a single sentence; this is called intrasentential codeswitching, where the language change occurs inside the sentence.
Bramlett, Frank, "A Different Kind of Bilingüismo" (2003). English Faculty Publications. 40.