Argentina
Buenos Aires porteño Spanish extends voseo into all casual registers — conjugations like 'quedás' (you stay), 'bancás' (you support), and 'estás' (you are) replace the 'tú' forms used across most of Latin America. Lunfardo, the historical Buenos Aires street slang, contributed lasting vocabulary through processes like vesre (syllable inversion: 'café' → 'feca') and heavy borrowing from Italian, Galician, and Yiddish immigrant communities in the late 19th and early 20th centuries. Many lunfardo words have since become standard Buenos Aires informal vocabulary, indistinguishable to locals from ordinary Spanish.