Spanish is now available, but only on the devices also sold in Spain or México.
You can buy echo dot 3rd gen, echo spot, echo v2, echo plus and they will have spanish as an available language if you have the latest version of the alexa app, but you cannot find spanish in the echo show or echo sub
I just bought my Alexa Echo v3 (configured in Mexico) and it works fine in mexican spanish, BUT it will be great that it can be BILINGUAL, (Spanish & English) because some features are still only available in english, like 3rth parties devices, so PLEASE make it bilingual, call one name for english (Alexa) and another for spanish (Axela) or detect it, it's a software easy solution. Thanks
Keep reading for newer answers, below. Spanish is now available on the Echo Dot 3rd edition. I’d call Amazon for how to download/choose this. It maybe available for update to other devices as well over time. If in doubt about tech issues, I always message or call Amazon. Best of luck.