It sounds like you've gone massively for breadth, at the expense of any depth. "We need users to help us grade the languages" sounds like you're asking people to pay you for the privilege of working for you. Why would I pay $10/mo, much less $100/mo, if I have to figure out for myself what content is good and bad?
What I want as a learner is for someone else to give me good, accurate content; I definitely want to avoid any content in the target language which isn't native-sounding, because who knows how long it will take those bad habits to break.
One idea I had for content was something like this:
1. Start with two languages; say, English and Chinese (the first of which I'm a native speaker, the second of which I'm learning); and focus on English speakers who want to learn Chinese, and Chinese speakers who want to learn English.
2. Start with some basic content in both languages; from Tatoeba, from wikipedia, whatever. And hire a few native speakers of both languages to review, validate, and rate content.
3. Give new users some amount of credit for free; enough for them to use it for a few months.
4. Once they're out of credit, they have two choices: They can either pay a flat monthly fee, or they can contribute back to the content: Writing new content, reviewing & validating content, rating content, etc. And people could do whatever mix they want.
5. Expand to other languages as you grow.
I definitely see the attraction of trying to use automation to expand as far and wide as possible, but I think that ultimately it's more important to start by doing a few things well than by doing 50 things poorly.