I don’t think that what you said isn’t nice. They focus their literacy on Torah subjects, Loshon HaKodesh and Yiddish. So their not being as literate as most Americans in English, which to them is essentially a foreign language or at best a second language, is nothing to be embarrassed about. No more than students in Korea would be embarrassed at not being as literate in English.
The Satmar Rebbe zt’l, in the 1950s, when hiring an English principal for the Yeshiva told the new principal that if you teach the students X amount of secular studies then your salary is $8,000. But if you teach them more than X amount of secular studies then your salary is $7,000.
So while it is possibly true that such a test will, as you said, cause many to not be able to vote. It is still an overall good as it will eliminate millions and millions of idiot American dropouts on drugs and gangs from swinging elections to whoever promises them the most benefits by raising everyone else’s taxes.