Dapperdan
If you are going to apply for a "retirement Visa" then the marriage certificate is not needed but if you decide to go for the "married to a Thai" visa then you will need it.
Once you get the marriage certifcate translated you will need to get it "certified" by the Ministry of Foreign Affairs" in Bangkok.
Then you would need to go to your local Amphur and register your marriage there.
Once it is registered you will then be able to obtain a TM22 form which Immigration will need as one of the documents presented when applying for the "Married Visa".
It may sound complicated and a lot of work but once you have done it for the first application it is quite simple every year after that.
You didn't say where you will be applying i.e. which Immigration Office you will be using. This is important as someone who uses the same office might respond and tell you exactly what they require.
I believe as there are many more documents required other than just the marriage certificate you will need to be multi tasking and start doing/collecting them all as early as possible.