Warning do not do review exchanges!! If you do that then your chances of going high on keywords or ranks will be hurt. When I have time I will describe some ways but for now look at my thread on free ways to promote android apps.
And why would that be? Having no reviews looks bad, some people won’t download the app without any reviews. Also I think if the text in reviews has keywords, it actually boosts your ranking for that word. The only reason I can think of is that people who install & review your app here don’t actually use it, maybe they don’t even run it once… But still, more often than not they don’t uninstall it right away and keep it for a while, so its not that bad.
You can do like 4-5 just to get the ball rolling but I see people doing like 20-30 review exchanges. No most of the time they uninstall quickly because they are doing review exchanges with other developers also and their phones get full doing review exchanges. Unless its an app useful to them, they will delete fast.
You need to translate this app into more languages if you want more downloads. At the moment it’s only english users you are targeting, but you need users from all over the world. Also important is to add the phrase “learn spanish” into your title, this is what most users search for. Translate it into a lot of languages and also translate your title. Someone from my country wouldn’t search for a spanish learning app in english.