There’s a lot to like here. It reminds me of this great article I read about someone learning French by reading Harry Potter many years ago. I can’t find the first reference to it, but it seems a lot of people take this approach now and numerous articles have been written about this method.
https://www.google.com/search?q=harry+potter+language+learni...

I was delighted to see that you even wrote about it yourselves on your blog.
http://blog.readlang.com/2014/03/08/learn-languages-with-har...

Your content marketing is great, but you don’t do it enough. Good startups ship both code and marketing efforts on a regular basis…ideally, you should shoot for something going out weekly.

It’s great that you shared your numbers, but snapshots are less helpful than data or information that shows momentum. When I’m trying to figure out if a company is doing well, numbers at a fixed point in time usually isn’t enough data to help me determine what the company looks like in the future.

Early stage startups should try for at least 10%/weekly growth on your core metric. If you’re not hitting that, make sure you’re only spending time/energy on tasks to hit those numbers.

Onboarding experience can use some work. There’s not enough guidance in the app to make me feel confident that I can use your site to learn a language on my own. For instance, when I first login, I had no idea what I was supposed to do first.

http://cl.ly/image/253K373i1M2Y

Even though I saw Upload Text button and the Web Reader link/button…I naturally clicked on the first story…which lead me to a page with even less guidance. I’ve never learned a language by reading and I couldn't find any help for best practices to using your site or how I’m supposed to turn this exposure into language proficiency.

Highly recommend reading Kathy Sierra’s article about how learning isn’t a push model. Might give you some ideas:
http://headrush.typepad.com/creating_passionate_users/2004/1...

The highlight to translate UX feels promising, but I found myself wanting a way to see the full english text side by side with the translated portion.

Why make me click twice to learn words through the flashcard interface? (tab then button) Also, if you want me to do it everyday, offer me a daily email or sms to practice. Each one of those emails is an opportunity to upgrade them down the road.

http://cl.ly/image/343r002E071K

Speaking of upgrade triggers, it sure feels like you make it hard to upgrade or pay right away right from the get go. I think it’s because you’re shooting to upgrade people who are using it the most. That seems way too nice. :)

As far as your feature list is concerned on the marketing side…they feel very YOU centric rather than USER centric.
http://readlang.com/features

I have to do all this work to figure out why the feature is better for me. If the copy is one step removed from me selling myself, it’ll be two steps removed from me being able to sell it to a friend.

Here’s a link to another Kathy Sierra article talking about focusing on helping users kick ass over showing off how you kick ass (she’s the best).
http://headrush.typepad.com/creating_passionate_users/2005/0...

I see on this page that you do have daily reminder email for flashcards…funny, I never found it when I was playing with it.

Anyway, hope this helps. Keep up the good work!