Y'all is the American informal second-person plural pronoun
Spanish: "ustedes" (formal) and "vosotros" (informal in Spain) or "vos" in some regions
French: "vous" is the standard, but informally there's "vous autres" in Quebec French
Portuguese: "vocês" formally, but "cês" informally in Brazilian Portuguese
German: While "ihr" is standard, some dialects use "ihr alle" or regional variants
Italian: "voi" is standard, but some southern dialects use "vujatri" or similar variants
Greek: "εσείς" (eseis) formally, but informally "εσείς όλοι" (eseis oli)
Russian: "вы" (vy) is standard, but "вы все" (vy vse) is used for emphasis
Arabic: "أنتم" (antum) is standard, with "إنتو" (intu) in dialects
I am most fascinated by Y'alls', a double possessive or possessive plural contraction which is common in Southern American English and AAVE (African American Vernacular English) which would otherwise be constructed more awkwardly in common American English as "all of your" or "your all's."