I was amused when welcomed aboard in Bahasa Indonesia - that I did not understand for sure hihihi ^_^ my friend translated it to me and to this day I can't remember what and how it... was said.
From Parapat, there is a port along the road where public angkut route around. It is very accessible and definitely easy to locate. Just ask the driver "Bang, tolong ya. Aku mau *pingger (aint sure of the spelling but pronounced as is) disana port ada ferry to Tomok... haissst this is not the exact sentence, but the driver will understand what you are asking help for (to drop you off at the port where you can get a ferry ride to Tomok Island) huuuuuu Aku ungga tau Bahasa Indonesia huhuhu (kalUrkie! I do not know how to speak the language, too heheheh!)
On your very first step on the ground, fish vendors are spread around the area. They do not mind even when their skin sizzles with uv as long as they get to sell their dried fish..
that meant.. the language (s) they used is the only language (s) they know. the LOcals do not speak BAhasa Ingrgris or English. So goes the challenge of communication. AT times, sign language helps but translation will always be a problem... @_@
Unique Suggestions: just say this: Aku ungga tau Bahasa Indonesia, then, terima kasih (thank you).
the skin color will definitely tell why ahihihih ^_^
Fun Alternatives: BETTER bring a local guide who speaks both languages, English and INdonesian.
Lucky us, we did not have to because a very close friend of mine (a sister) volunteered to go with us. She knows what we will be getting into if she just lets us go on our own.
There is one VTer based in Medan that you can contact though. She speaks and understands English. Check on VTer Vina (Medan page on VT)