Spanish phrase
¿En qué idioma debo ~?
Meaning
In what language should I ___?
When to use it
Asks which language to use for an action. Used when choosing how to reply or speak depending on the recipient; neutral, polite.
Example dialogue
¿En qué idioma debo responder a este correo?
In what language should I reply to this email?
Mira quién lo envió; si es extranjero, respóndele en inglés, si no, en español.
See who sent it; if they are foreign, reply in English; if not, in Spanish.