In topics with multilingual/translated posts (like mine above), you’ll now see a 
button at the top of the topic right-hand sidebar. This will allow you to configure your language preferences:
If you add Spanish to a language you understand (or untick translation), you’ll see my shoddy Spanish directly. You can also configure this in your interface preferences directly.
We may in the future add more supported languages (or turn this back off) but this seems like a great way to dip our toes in the water here. Let us know how it goes!
Do note that due to a Discourse limitation, you can’t directly declare your post’s language as you author it with the “Post language” selector — you just have to leave that unset and let the auto-detector detect it for you. You can change it later if it gets it wrong.