The people in Lachen speak hindi. Some of them understand english as well
There are sumo/mahindra maxx available from Gangtok to lachen. One may either book a whole sumo which will cost them around 15000 to 20,000 approximately (bargain for a good price here) this price includes food and lodging or may opt for a sharing package which cost around ~3000 per person, 10 people vehicle. These packages include Lachen and Lachung. Permit has to be taken one day prior for it. The trip may get cancelled during land slides however sometimes permission for transfers between the land slide points are allowed.
Lachen is covered as part of North Sikkim Package tours. This is the transit point for visiting Gurudongmar lake. This lake is the 2nd highest lake in India. Restricted area permit is required to visit this lake.
Package tours to Lachen, Lachung, Thangu as well as Yumthang Valley is conducted by :
Mobile : +91 9903295920 Phone : +91 033 26270886
This agency takes care of all your requirements like acquiring Restricted area permits as well as transport to Lachen and the entire North Sikkim.