Procedure to marry a foreigner in India

Hello. I am from Thrissur, Kerala. I want to proceed international marriage under Special marriage act. My fiancée is a Japanese citizen and currently staying in Kerala with e-tourist visa temporally. I have inquired my local marriage registration office about procedure and required documents. They told to first apply online and submit the document online as well. I have asked about the needs of Authentication / apostille (apostilization) of documents from Japan but I could not get a clear answer from them. It seems they are not so aware of international marriage procedure. So I would like to ask about the required documents and procedure. I believe my fiancée has to submit 2 documents from Japan. A birth certificate and no objection letter (marital status certificate) No objection letter (marital status certificate) can be collected from Japanese consulate in India and it will be in English so I think this is ok, not a problem. However, she has to collect a Birth certificate from Japan which is only available in Japanese language. So she has to submit an English translation along. Question; 1. Since Birth certificate is in Japanese language, does it have to get authentication or apostille (apostilization) from Japanese government? 2. Only birth certificate needs authentication / Apostilization ? Or translation document also has to get authentication/apostilization? (Apostilization for birthday certificate and translation both?) 3. After authentication or apostilization by Japanese government, do we have to also get aithentication from Indian Embassy in Japan to prove it is an official document from Japanese government? (I hope this is not required because it will take extra time ) I would like to proceed soon as possible while my fiancée is still in Kerala. and in this present situation of covid, it is not so easy to collect documents from Japan, so I would like to make it without any troubles and prepare correct documents at once. 4. I also would like to know the procedure and how long it will tatke once we submit application. Thank you so much for your kind answers in advance.