Spouse VISA to US - translation issue

Hi. I'm a US citizen, and I've been married to my Japanese wife for a year now. We got married here in Japan and have been living here for the past year. I'm trying to file an I-130 petition for my wife.
As for the marriage certificate, the US embassy web site says that they will certify my English translation for $30.
But for the VISA documents, it says that the translator must certify that he/she is competent to translate the foreign language into English.
I need my wife's koseki translated into English. I feel competent enough to translate it myself, but I don't have any certification. Has anyone done this translation him/herself? How can I prove that I am competent to translate this? Or can I? I do have level 1 JLPT certificate from 4 years ago, if that helps at all.

And another thing. My wife changed her last name to mine. Anyone know if there is any complication in that?

Thanks in advance.

You can translate it yourself. We are going through this ourselves right now with an attorney. The problem is this, it has to be EXACT WORD FOR WORD...not a generalized translation, absolutely zero errors allowed. You have to sign a statement swearing that you are able to translate the document. However, since you have a vested interest it may cause suspicion and the US department of homeland security can choose to deny your request based on your translations and require you to have a "real" translator re-do your work. Our attorney has had several cases denied until a certified translator did the work. It's a personal choice and we didn't want any troubles so we had all of our documents translated and certified. It's not much money and it's worth the piece of mind. The US doesn't give you your money back for a "do over". So once you pay and if it's kicked out you get to have it translated and your get to pay to re-file. Ever since 9/11 they have gotten much more picky. For the Koseki we sent it to a translator in Tokyo and it took less than a week and it was around 30 dollars (if my memory is correct!) I guess when you are dealing with the time and effort and expense of a Visa, it's safer to have a translator. Not sure if this helps, but I go by the old adage "better safe than sorry.".

Thanks for the info.
I guess then I'll look for a certified translator too.
Shame though...