The population of Lombok which is the next island to the east of Bali is a tiny 3,000,000 people who are spread over the 4,725km2 of Lombok's land although the majority of the people are concentrated around the west of the island around the capital city of Mataram and the port of passage to and from Bali named Lembar and the north tourist resort area of Senggigi leading up to the Gili Islands. It is in these areas that the most of the jobs are orientated and in the west and around most of the south of the island there is very little opportunity for people and the people are a lot poorer. The people of Native people of Lombok are known as Sasak people who are Muslim and make up the firm majority of the Lombok' Population. There is also a Balinese Hindu minority that is estimated to account for less than 10% of the population who appear to integrate peacefully with the Sasak people despite the years of vicious history between the two islands. However you often do not need to delve deep before bringing feelings of resentment up from either side although this seems to be a fading thing affecting only a handful of the population.
The only other ethnic groups include Chinese, Arab, Javanese and Sumbawanese who are the decedents of past invaders. When traveling in the south it is easy to see how the surfer's village of Kuta is only just growing up from the dust and there are still very few facilities in the area. The surfers who stay there generally wake up early, and go to bed early meaning there are a few places to stay and a few restaurants but no development of resorts or at least not just yet. It is easy to see who Kuta has prospered from the other areas of the south of Lombok where the poverty is stronger, however there retains a pleasant attitude among the people who are mainly farmers and fishers who work on Lombok's soils that are far less fertile than that of Bali.
The Sasak Language is completely different to that of the Balinese and is said to have developed from the interactions with Bali, Sumbawa and Java and does have some similarities to each of these languages. However many people understand the modern Language of Bahasa Indonesia which is only just over 50 years old and Is based on the Malay language so if you are traveling in Indonesia and would like to pick up a little lingo then Bahasa Indonesia is the best option however you will be even more appreciated if you learn a few of the basic phrases in Sasak.
Festivals and cultures do differ strongly between the Balinese Hindus and the Sasaks who worship completely different gods and ideas. This does give Lombok diversity in its population although if you are traveling in both Bali and Lombok then it is more beneficial to Experience the Unique Hinduism in Bali and the Sasak Culture when in Lombok.