Provided you stay away from military zones, there are few safety concerns in the region. Theft is uncommon.
The journey to Gurudongmar is into very high altitude and cold zones. Many people experience headaches because of lack of oxygen. Don't exert yourself too much and drink lots of water. If you are having kids with you, please be careful. The roads are steep and winding and nausea is very common.
talk
English is widely spoken, most of the guides and drivers understand Hindi as well although Nepali is the most widely spoken language.