The history of West Kalimantan can be traced back to the 17th century, when Dayaks was the original inhabitants. The Malay migrated to West Kalimantan and built their own sultanates. The fact that there is a significant Chinese population in this province was that there used to be a republic built by Chinese miners called 'Lanfang Republic' after it defeated the local Malay sultans. The government of Lanfang Republic was overthrown in West Kalimantan after the Dutch occupation in 1884. The Japanese occupied West Kalimantan from 1942 to 1945 until Indonesia declared its Independence.
West Kalimantan was the site of substantial fighting during the Indonesia-Malaysia 'Konfrontasi' (Confrontation) under the Sukarno government in the mid-1960s. After Suharto deposed Sukarno in 1965, the confrontation was quickly resolved. Domestic conflict continued, however, for another ten years between the new military Suharto government and fighters organized during the confrontation and backed by the banned Indonesian Communist Party (PKI).
As elsewhere in Indonesia, Bahasa Indonesia or Indonesian is the official language. The young teenager can speak English too.
There are three majority races in West Kalimantan. They are Malays, Dayaks, and Chinese. It's better to use the word Tionghoa instead of Chinese or China when talking. The Malays usually use their own Malay dialect. The vocabulary is almost like Indonesian official words. It's only the speaking intonation only and some vocabularies replacement.
The Dayaks people have their own dialect like Kahayan and Ot Danun.
The Chinese people in West Kalimantan speak various Chinese dialects like Mandarin, Teochew, Hakka, and Cantonese. Some old people, who learn in pre-Indonesian-independence school, can even speak Dutch or German.
Knowing some phrases in local dialects will greatly impress your hosts.