HI, playing with audio prompt I've detected that, at least on the test page, navigation instructions are spoken in english when spanish language is selected. I don't know if there' a more formal place to report bugs so put it here.
I had a similar issue, having the prompts in english AND in german. The problem in my case was because the app garmin connect had one language and the garmin edge had another. Having both in the same language solved the problem in my case.