If you're serious about learning a language, and it's a tool that you're going to use every day that actually helps you learn, then $25/mo is a good deal.
I pay $30/month for FluentU.com just to watch embedded Youtube videos with the Spanish transcription beneath it as it plays:
ReadLang.com ($5/mo) has much better tech for video transcriptions (Google Translate API can translate idioms and phrases like "lo que ..." instead of only individuals words).
An idea for OP is to split apart text and video as a first-class distinction in the Library UI. I didn't even know ReadLang had videos until I was already a subscriber - I thought it was purely for text and websites.
If you can boost the amount of video content, I imagine you can boast about your video transcription offering like FluentU.com does which is the reason they got me to pay $30/mo to them.
One thing I like about the language-learning field is the subscription model. Living in Mexico, I was paying $15/mo for Fluencia.com without actually using it. "Why would I cancel? Surely I'll start learning Spanish any day now!" I finally buckled down and starting hitting the Spanish hard and ReadLang is an essential part of my kit.
Steve - For the love of god, do not listen to any of this! You should 2x or 3x your prices.
Focus on the users that get the most utility out of the product, and relentlessly focus and optimize for them. There's plenty of value there for people that truly want to learn another language. These price comparisons to Netflix are comically misleading.
I agree that the value isn't there for $25/month but charging $5/month isn't going to make him any money either. I would change this so customers get one (basic) lesson per language for free then have to pay to keep going. For that I would charge $75 for the year on each language. That would be a small bump on the annual but he'd be getting paid up front.
Where his pricing is now is good, and I'm seriously considering getting on board.