Whenever two people meet, negotiations take place. If they want to express solidarity and sympathy, they tend to seek common features in their behavior. If speakers wish to express distance towards or even dislike of the person they are speaking to, the reverse is true, and differences are sought. This mechanism also extends to language, as has been described by Howard Giles' Accommodation Theory. 

Some multilinguals use code-switching, a term that describes the process of 'swapping' between languages. In many cases, code-switching is motivated by the wish to express loyalty to more than one cultural group, as holds for many immigrant communities in the New World. Code-switching may also function as a strategy where proficiency is lacking. Such strategies are common if the vocabulary of one of the languages is not very elaborated for certain fields, or if the speakers have not developed proficiency in certain lexical domains, as in the case of immigrant languages.

This code-switching appears in many forms. If a speaker has a positive attitude towards both languages and towards code-switching, many switches can be found, even within the same sentence. If, however, the speaker is reluctant to use code-switching, as in the case of a lack of proficiency, he might knowingly or unknowingly try to camouflage his attempt by converting elements of one language into elements of the other language. This results in speakers using words like "courrier noir" (literally mail that is black) in French, instead of the proper word for blackmail, "chantage".

Bilingual interaction can even take place without the speakers switching. In certain areas, it is not uncommon for speakers each to use a different language within the same conversation. This phenomenon is found, amongst other places, in Scandinavia. Speakers of Swedish and Norwegian can easily communicate with each other speaking their respective languages. It is usually called non-convergent discourse, a term introduced by the Dutch linguist Reitze Jonkman. This phenomenon is also found in Argentina, where Spanish and Italian are both widely spoken, even leading to cases where a child with a Spanish and an Italian parent grows up fully bilingual, with both parents speaking only their own language yet knowing the other. Another example is the former state of Czechoslovakia, where two languages (Czech and Slovak) were in common use. Most Czechs and Slovaks understand both languages, although they would use only one of them (their respective mother tongue) when speaking. For example, in Czechoslovakia it was common to hear two people talking on television each speaking a different language without any difficulty understanding each other. Another example would be a Slovak having read a book in Czech and afterwards being unsure whether he was reading it in Czech or Slovak. This bilinguality still exists nowadays, although it has started to deteriorate after Czechoslovakia split up .

Multilingual individuals
Bilingual model
Coordinate model
Multilingualism between different language speakers