Do I need to translate my affidavit of income and is a police clearance required for a 1-year extension based on marriage in Thailand?

Why would you need a bank letter and bank book if you have the embassy income letter?

IF you are from one of the country's whose consulates still issue the affidavit of income from abroad notary letter (which should be in english) you don't need to get it translated. AND as far as whether you need a police background check to get the year extension based on marriage (or anything really) that is more down to your nationality than anything else. I would hazard a guess and say NO you do not need the background check, just the TM7 application for extension, the thai marriage documents (possibly updating the Kor Ror 2), the required photos of you and your wife, the letter from your embassy stating you get a minimum of 40K baht a month in income, hand drawn map to your house, etc <- NOTE that is only a partial list of what you actually need and it's the reason we tell people to make the trip to the immigration office with your thai wife in tow BEFORE you show up to apply for the year extension. That way you know what you need and are not caught with missing documents on the day you go to apply