Learning a language in two ways
You can take a course of Spanish for English speakers, and you can learn Spanish that way. BUT can't you take a course of English for Spanish speakers? Sort of the same thing right?
If you try to learn Spanish by taking the English via Spanish route all the audio will be in English - a big disadvantage!
Even though English is my native language, I'm doing the English via Portuguese course for fun after completing my Portuguese tree. I'm always caught out by the transcription exercises, though, because I listen to the sentence in English and start typing away in Portuguese only to be told my answer is in the wrong language (typing in English based on English audio is too easy even with the robotic voice).
In answer to your other comment. You are right, as I said, I hoped there would be more translations in the direction I find more challenging, that is from English to Portuguese in my case. I can often get the gist of what a Portuguese sentence means in English, but coming up with a grammatical sentence in Portuguese is not so easy and is obviously a skill worth practising.