As a language learner, I love what you have going on! However, I have a suggestion. As a learner of Arabic, it can be quite a challenge to find good learning materials. When I saw your TurtleTube feature, I was immediately excited for it. However, after looking through it for a bit, the engine behind it seems to be quite flawed (at least for Arabic), featuring lots of content with only a few lines of subtitles (in a 14 minute video) or with subtitles that don’t match the language (Arabic subtitles under an English song, for example).
I feel this issues could be easily circumvented by making it easier for the community to contribute to the lists. Leave the engine there to gather videos, but add some buttons to allow the community to upvote/downvote videos and make suggestions for the appropriate level. This way, the TurtleTube library could be expanded and improved with relatively little work from the devs’ side (I would be more than happy helping out by rating content for my native and proficient languages, and I’m pretty sure I wouldn’t be the only one).
Keep up the good work!