According to Wikipedia Spanish is the second language by number of native speakers (5.85% of world population), followed by English (5.52%), while German ranks 11th with 1.39% of world population. Nevertheless Germans can talk to Alexa in their own language. Adding Spanish language support would just seem sensible since there is an Amazon.es website alongside a German Amazon.de, not to mention the large number of Spanish speaking individuals in the US.
Although English acts worldwide as a lingua franca, the very concept of Alexa points to the convenience of addressing an Echo device as a personal assistant without adding the stress of a foreign language. If the device is not easy to address in the user's native language there seems to be no point in the very existence of Alexa, the user could just sit down and get on the Internet with a tablet, a smartphone or a PC. Alexa's main point is convenience.
I have little doubt a team of volunteers could be set up in order to address the necessary linguistic issues, and I guess Amazon could be quite interested in expanding the Echo market to Spain and Latin America. The demand is out there, it's just a matter of providing the adequate supply.