Good spot, I can confirm that the string is not internationalised on line 126 of mintInstall.py I'm not sure how to bring this to their attention though, hopefully being here is enough.
Basically anything that is to do with a mintTool you should bring up here, and you can help translate it. If it's not a mintTool, like the examples in compiz you mentioned earlier, I'm sure they'd be glad for the input, you just need to find the right forum!
If you have a question that has been answered and solved, then please edit your original post and put a [SOLVED] at the end of your subject header
Hint - use a google search including the search term site:forums.linuxmint.com