Language is an arbitrary speech symbol including words, sound, and meaning. In effective communication, the main focus is two way communication which contains understanding the discussion topic between speaker and listener / sender and receiver.

Apparently, accent is not part of language aspects. This term rises when different group of people speak other languages. For an example, Indonesian people speak English. You will notice that their will have different accent comparing with English man. Their spoken English is affected by their mother tongue

The accent term also rises when some group of people speak the same language such as Britain, England, and Australia. You can read it in some dictionary which has those three accents. I think that it happens because of the self identity exposure. We can directly state that those people is English only from their accents. 

Learning different accents are important because it will ease you to dissolve with certain group of people. When you speak English with British accent in England, it will help you get along with people and make new friends