It is in Tibetan language.
The biggest set is 170 m wide, 50 m tall.

It’s the six letter mantra of the Buddha of Compassion, or AVALOKITESHVARA. It goes, Ohm, Ma, Nih, Pedh, Meh, Hung. This is sort of the most widely recited Mantra by Tibetans, and you will find this even carved on stones everywhere in Tibet.