Why? To stick it to them filthy welfare-sapping spicks and latinos mojados? And why aren't we seeing these measures proposed in areas where they speak a lot of Vietnamese or Polish?
But seriously--there's no reason for the government of a free society to not put out official forms in the language of the people it serves, whether that's English, Spanish, Farsi, or Klingon. Having applications for drivers' licenses, voter registration forms, and the like available in the native tongue of a group of people present in this state in substantial number is a matter wholly separate from English's social status as our common language, which is the pretended purpose to this Constitutional amendment.
Fortunately, this is almost mere symbolism, as it has so many exceptions--foreign language instruction, commerce, tourism, law-enforcement, public safety, criminal defence, international trade--that it's difficult to think of a situation in which it applies. Of the several ballot-measure manifestations of Arizona's newfound whitebread xenophobia, this is the silliest. Nonetheless I oppose it due to its spirit and intent and on a desire to keep superfluous articles and evidence of ephemeral hysterias out of the State Constitution.
In case your stomach was churning at the thought, the foreign-borrowings clause means that even if this passes, students in public schools can still be served burritos instead of "wraps."