Speaking about language spoken in the city of Medan we con not refer to certain dialect or language, since the population of the city is mixed. Some speak Javanese, Some Chinese Indian and Arab. But every one speak Malay and Nationalized Malay the Bahasa Indonesia. The Batak speak their own with their 4 main dialects as a result of geographic influence and long isolation, but when communicate with others Malay or Bahasa Indonesia is their only means. Between Malay and Bahasa ha Indonesia has little differentiation in the pronunciation, which ks last vocal and small nuances of certain words. When one visit West Sumatra will hear how Malay is spoken, or in the province of Riau and Malaysia, where it is believed to have been the first place of Malay language development. At the places such as tourist destinations, hotels, nd restaurants, English is the most widely spoken, while in public areas it is difficult to find some one speaks English or foreign language. Quiet different at the places of travel destination such as Bohorok, Berastagi, Parapat and Samosir island, where one is easy to find people speak simple English.

First travel organization in North Sumatra was initiated by Dutch tourist and continued until late 1980s in an influx of big groups, so among older people still can speak Dutch, further more those generations of 1940s who might still alive today, they mostly understand spoken Dutch. For individual own arrangement travelers it is worth to learn some phrases of Bahasa Indonesia to prepare that they might need to communicate at the places where no one speak English or foreign language. In the destination such as Berastagi, Parapat and Samosir island some people even can speak simple language of French and German and these people tend to work individually as tour guide and always urge guest by offering their service to whom you if don't wish to politely refuse with very clear reason.

For those who really wish to involve with local people without the tour guide some local manner must be understood a little bit to avoid miss understanding which can caused problem during your travel and at last damage your holiday. The basic conduct for Indonesian people are used here, except the Batak a little bit open in their daily communication. But this openness not necessary the same as Western world, still within the frame of Asian people since openness is not considered polite, there are so many words to disclose the inconsistency, of one's attitude or misfortune, disagreement or negation. Usually expressed in the accordance of agreement first than suggesting another answer.
Call or address one's name who is older or not known is not common. It is suggested to put " Pak " for man and " Bu " for woman of older age and unknown. Once it is known call Pak / Bu followed by the name would be the most refine accost.
Shake hand, point something by left hand is not considered polite. Basically using left hand to indicate to some one is to be avoided.
Point something by foot is totally unacceptable and is considered humiliation
Touch one's head unless you are older and have been acquaintance with the person is considered not polite.