People stop using them. Suppose for example your country with its unique language is conquered and made part of a giant empire with a different language as standard. Everyone learns the new language and you teach your children both your first language (which you are most familiar with) and this new language. They grow up being competent in both to nearly equal degree.
Time passes and your country is filled with visitors and transplants from elsewhere in the empire with their own languages of origin. But they all speak the language of the empire so people tend to use that more than anything else. Over time they get more familiar with the empire’s language and use of the old local language decreases.
Eventually the last competent speaker of the old language dies and so effectively does the language.
Latest Answers