Siri is not available in Spanish for LaitnAmerica, only Spanish for Spain. If your region is not set to Spain, Siri will not be available.
Siri no está disponible en Español para Latinoamerica. Solo en Español para España. si tu region no esta determinada como España Siri no estara disponible.
Use Siri on your Apple TV (4th generation) - Apple Support
Siri is currently available on Apple TV (4th generation) in these languages and countries: English (Australia, Canada, UK, US), German (Germany), French (France), Spanish (Spain), Japanese (Japan).*