Sorry, but it's been done. In the Sandoval case, the US Supreme Court ruled that citizens could not to sue to force an interpretation of Title VII of the Civil Rights Act (which permits effects-testing of possibly discriminatory policy), that Alabama's official-English policy of no foreign-language drivers tests was not covered by Title VI (which bans intentional discrimination), and the majority opinion even suggested that language could not serve as a proxy for national-origins discrimination outside of the very narrow interest of childhood education.
>> He cites guidelines from a 2001 U.S. Department of Transportation notice which states in part that "assertions of safety justifications" of the kind made in support of the English-only drivers' test bill "would generally not be accepted unless accompanied by statistical and/or scientific causality studies showing a positive correlation between limited English proficiency and crash/injury rates substantially higher than would be expected due to chance." <<
The Department of Transportation has no power to enact legislation, and its guidelines were merely guidelines: they suggest that the government MAY decide an official-English policy is using language as a proxy for national origins (even though during the Civil Rights debate, a young Sen. Kennedy insisted that "national origins" means where you were born, not language you speak, so Bush is full of sh!t with his opinions... to the left of Kennedy AGAIN!)
If DOT WANTS to sue, it's the DOT's prerogative. They will not because they know they would lose in a heartbeat, and have their de-facto law overturned by the courts AGAIN. And no citizens' groups can compel them to sue.