Additional game tweak - force environment variable button in settings

[whoozle]

Steam could enforce command line switch with "set launch options..." button, but could not force some environment variable such as LANG. This would be very helpful with games trying to parse floating point numbers in non-english locales (0,5 instead of 0.5 often leads to parse errors/exceptions).
I know that at least two games affected by this: Kentucky Route Zero and Bionic Dues. (All mono games are affected too)
So, setting environment (LANG=C/en) could work-around parsing problems. This could be either LANG modification button or generic environment variable dialog box.

Thank you for your time