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.

I am a professional translator, but not certified by any country in legal document translation. If I get any inquiries from potential customers who wants documents of that nature, I refer them to embassies - so that the embassy can at least certify (like notarize) the translation that someone like myself has done, or even better, the embassy can supply them with a list of their certified translators.

As for the name change, (no lawyer here but as far as I know) as long as there is consistency - meaning, her koseki notes that she has changed her family name, and her passport reflects this - it should be no problem.

Thanks for your input. I'll go ahead and translate this thing myself and bring it to the embassy to notarize it, if they'd do that for me. If not, then I guess I'll just have to go and pay a certified person to do it.