When studying linguistics, the term diglossia denotes the existence of two dialects of the same language spoken in a single geographic area. Occasionally, it will refer to two languages such as Spanish and English spoken in the same area with speakers switching between one or another according to their needs. This would be true in many metropolitan areas around the world.
When two dialects of the same language are in use, one of them is usually the formal version of a language used in education, and by those who are educated while the other is the more common dialect of the language. When this occurs, it can create or perpetuate class differences. Diglossia is common in Arabic and Indian cultures where it can cause difficulty when people are acquiring language skills or when they move from one area to another.
Thanks, and what are the short-comings?
If someone is attempting to acquire language skills, diglossia can create difficulty in the learning process. Also, the different dialects can signal whether a person is educated or not. When moving from one area to another, the different dialects can present challenges even for native speakers since the nuances of the language dialects are different. Therefore, diglossia can limit mobility and signal one's education or lack thereof in a society. There are times when native speakers use one dialect for formal situations but use the less formal dialect in social situations in an effort to be accepted.