Seems pretty damn straightforward to me. All road signs and markings are in English - the test should be in English. If you cannot read English, then you should be treated the same as someone who cannot read - no license for you. Operating a motor vehicle on public right-of-way is a privilege, not a right - the requirements regulating that privilege are pretty damn basic and simple. Lack of fluency in English is not some handicap that can't be helped or overcome.
What language are all legal documents written in? Aside from the obvious such as the pesky old Constitution, Declaration of Independence, Bill of Rights, etc., how about bills in Congress? AWK, would they allow you to submit a brief or argue a case in any language other than English?
Why stop at only 11 or 12 languages for the test - what if I want it in Swahili or Klingon (or is that already one of the 12)? What if someone gets offended because they consider Spanish to be the language of their European oppressors - maybe it should be written in Nahuatl or Maya script?
After seeing how much my partners and I are spending for H1b/green card stuff for one of our engineers who grew up in Asia (doing it the right way, legally), I have no interest in going out of the way to accommodate someone who is in this country illegally. Italians, Germans, etc. knew when they came (legally) through Ellis Island that they needed to learn English to assimilate into the existing American society and commerce.
You make an exception for one non-standard language in Spanish, then there really is a discriminatory distinction relative to the next largest groups like Portuguese or Russian or whatever. English-only is a matter of standardization and practicality, not discriminatory.
Bottom line - if you can't read English you can't drive, so stay your ass in the back of the pickup