Ok this is what I found...
Non Tongan passport holders who wish to get married in Tonga.
There is a law that anybody holding a visitor's visa in Tonga (i.e. foreign passport holders), must apply to the Principal Immigration Officer (Minister for Foreign Affairs 聳 address see below) for permission to marry (Section 10 of the Immigration Act).
NB: If a person holds a valid visa (Not a visitor's visa) s/he is quite free to marry in Tonga without going through these formalities.
Procedure
The non-Tongan passport holder lodges a letter with the VISA Section of Immigration stating that s/he is a citizen of (whatever country) and wishes to marry a Tongan subject in Tonga (or a foreign subject in Tonga).
S/he must submit an affidavit (a statement on oath) stating that s/he is free to marry, has no criminal record etc; The affidavit may be done in Tonga or if done overseas, the original must be signed by a notary public.
Their passport must accompany the application
Application fee of T$5O.OO (if it is two foreigners wishing to marry in Tonga and both have visitor's visas then the fee is T$50.OO each)
If the person is marrying a Tongan subject - we require the Tongan subject's Birth Certificate or Tongan passport with the application.
Both applicants need to have their original Birth Certificates for the Registrar of the Supreme Court (Not the Immigration division) for the Marriage Certificate.
The whole process can be completed within 2 days or less.
Address of the Ministry of Foreign Affairs in Tonga
Ministry of Foreign Affairs
PO Box 821
Salote Road
Nuku'alofa, Tongatapu
Kingdom of Tonga
Phone: +676 23-600
Fax: +676 23-360
