Translating your own work using GoogleTranslate is not plagiarism, any more than hiring someone to translate your work would be considered plagiarism. (In the latter case, you would insert a line stating "translated by...")
While Google does store what you write, it's not a dump of "everything ever written in any form by anyone" that plagiarism-detecting tools later go over. Instead, there is "everything published online", which Google doesn't store, merely indexes so it can be found. Software searching for plagiarism would be going over (a subset of) that. And there is the stuff you've entered into Google's search line. Some of it, Google stores. And does analysis on. But it's not really accessible, except in aggregated form - "N people this year searched for X". As for what people search to translate, I'm not sure Google stores that at all, but if they do, it would be in the same sort of "bucket" as the searches - not the "bucket" plagiarism-detecting tools would search. (Somebody more tech-savvy is more than welcome to improve on this explanation.)
As @rasan076 points out, there's always a human at the end of the line, reviewing what the software spits out, and figuring out whether there's really any plagiarism. Since you hold the original work, it is very clear that there isn't. Basically, it's your work. You publish it online, you do whatever with it, it's still your work. No plagiarism.
Only problem you might run into is, Google Translate is not a very good translator. Your sentences might well lose their original meaning, or any semblance of meaning at all.