The Tongan word for "welcome" (and general greeting) is:
Malo e lelei
Pronunciation: MAH-loh eh LEH-leh (stress on first and third syllables).
Literal sense: "Thanks for being well" or "Goodness to you." Used for hello, welcome, goodbye, thank you — context-dependent.
Related:
Tongan (lea fakatonga) is a Polynesian language spoken by ~100K in Tonga and diaspora (NZ, US, Australia).