Dialects, like accents, have a role to play in English as a second language courses because they have to do with pronunciation in a tongue which is not native to the learner. A dialect is usually spoken by people who live in a certain region of a country. Dialects are also noted in big cities where ethnic concentration or social and economic factors have lent to these communities speaking in a distinctive manner, that is, having a dialect. Those people speak their mother tongue in their own individual way. For example, many Scottish people have a dialect. There are regional dialects in the USA, as we know that Texans speak very differently to people from the Bronx in New York, and Minnesotans speak a different dialect to Bostonians.
An accent usually describes the way people pronounce words of a language that is different from their mother tongue. For example, Arnold Schwarzenegger speaks English with an Austrian accent.
dialects versus accents
A variety of language, spoken in one part of a country (regional dialect), or by people belonging to a particular social class (social dialect or sociolect), which is different in some words, grammar, and/or pronunciation from other forms of the same language. A dialect is often associated with a particular accent. Sometimes a dialect gains status and becomes the standard variety of a country” (Longman Dictionary of Language Teaching and Applied Linguistics, p.107).
Many English language learners find that they understand a standard dialect which is commonly heard on television, radio, and most native speakers around them. Dialects become unintelligible however when they also consist of slang and colloquialisms which are peculiar to that region or sub-culture. If the learner is not consistently exposed to this dialect, there will a difficulty with understanding it. However many native speakers are unable to make meaning of certain dialects, too.
The most practical attitude an English language learner can have is to focus on the English that is spoken around them, and that is taught at the ESL school and not to worry about understanding dialects unless they are planning to spend some time in those regions!