It is almost not possible to learn a foreign language without learning its culture. Or other way round, you will learn its culture when learning a foreign language. Language is a bridge of culture and people as well.
According of the Department of Education and Culture of Republic of Indonesian, Indonesian culture consists of a variety of cultures of ethnic groups in Indonesia. Indonesian culture represents a totality of cultures such as wayang kulit from Central Java, ludruk from Eastern Java, pantun from West Java, gamelan kebyar from Bali, pustaha literature from Batak and so forth. The competence of the regional language is indispensable to appreciate and understand deeply a certain genre of performing arts.
Although some observe that nowadays regional languages have become less important in daily life than before, it does not mean that people in Indonesia do not use regional languages. In the daily life of Indonesia, people often unconsciously and sometimes consciously mix up their regional language which often can not be substituted by Indonesian equivalents. Such words or expressions often constitute key words explaining unique cultural value and significant words expressing their emotion.
Indonesian, the national language of Republic Indonesia, is widely used especially in the cities and considered to be more useful for foreign students in terms of communication and accessing local information. However, the importance of regional languages is greater yet in the countryside. Some of older people do not or cannot speak Indonesian. In such a socio-language condition, a regional language is indispensable for someone to undertake fieldwork. If one wants to hear the voice directly from the people of every stratum of a community, one needs the command of the language of the community. I think that it is one of the important missions for educational institutions to train promising researchers who will be able to communicate with the people in the field.
The knowledge of regional languages not only will enhance your competence in Indonesian but also help you to understand Indonesian culture better.