It’s Saturday afternoon at Doug Winter’s cafe, in El Paso, and Eduardo Bouché, a linguist in a black baseball cap, wants the students in his English as a Second Language class to hear the different pronunciations of vowels. His hands flow like a choir director’s as he teaches. He writes the words “eat” and “it” on a small chalkboard propped on a table and asks each of the students, from 6-year-old Teo to 72-year-old Annamarie, to say the words. “Relaja la boca, relaja la boca,” Bouché says each time they pronounce “it”; the short i, nonexistent in Spanish, is easier to say when the mouth is relaxed. When it’s my turn, he says, “Now listen, everybody, here we have a native speaker.” I stand and…