Go into your registry. If you have an x86 operating system to:
HKEY_LOCAL_MACHINE\\SOFTWARE\\Bioware\\Mass Effect 3\\
on x64 to:
HKEY_LOCAL_MACHINE\\SOFTWARE\\Wow6432Node\\Bioware\\Mass Effect 3\\
I have an x64 Win8 so I'm not 100% sure the x86 path is correct, but it should not be hard to find anyway.
There is an entry called Locale.
Enter your desired country code. e.g. en_US, de_DE, etc...
I'm not sure which languages are supported and working though.

German and English worked for me without problems though and I did not need to download anything for it to work. So at least English localization seems to be shipped with my German version.
Changing the locale changes text as well as sound. I'm not sure if you can change only text or sound.