Not marketing advice per se, but I highly recommend subscribing to Hack Design [1] and giving more thought to not just the visual design and presentation of your apps, but also the audience. My personal opinion is that non-game indie devs need a niche, what's yours? If you're selling to school kids, then find a good hook. For example, public middle schools in California require Spanish fluency. Sell to the parents of those kids perhaps? Or if you're going after the international tourist, try to combine the language skills with travel info some how: "We'll teach you Spanish before you're plane lands!"

Also, I'm sure I'm not the first one to say it but you've gotta move to iOS7. Do the easy thing and try using all native color scheme. As a design exercise [2] it will help you focus on content.

Good luck!

[1] http://hackdesign.org/ [2] https://medium.com/design-ux/7348987453e3