Disculpe,
¿tiene
esta
camisa
en
talla
mediana?
dees-KOOL-peh, TYEH-neh EHS-tah kah-MEE-sah en TAH-yah meh-DYAH-nah?
Excuse me, do you have this shirt in a medium?
Latin American clothing sizes often use S, M, L like the US, but asking in Spanish shows respect.