Tongan is the national language of Tonga. It is a member of the same language family (Polynesian) as Niuean, Hawaiian, Maori, Samoan and Tahitian. It is spoken by roughly 130 thousand people in at least 7 territories.
After Tonga, the largest population (around 24 thousand) is in the United States. Other smaller populations are in New Zealand, Fiji, the United Kingdom, Samoa and Australia.