Firstly, it's not a marriage visa, but a Thai spouse visa.
In my passport, they wrote ภรรยาไทย ปีที่ 6 or Thai spouse, sixth year.
Secondly, it often depends on the local immigration office, and of course on your home country.
I come from Belgium, and the immigration office accepts an Affidavit from my embassy, the document is written in English.
It all also depends on your revenue source. If you have a regular pension like me, you also could ask your bank to give you a certificate. In that case, it's recommended to have your bank agency close to the immigration office.
Or, as someone suggested earlier on this thread, you can have a 400 k THB deposit on your bank account.
I've never been asked to provide translated documents, except for my marriage.