Hey thanks :) I didn't submit it yet in HN but tried to do so in more relevant communities such as /r/languagelearning etc. Buuuut, HN surely has a lot of people interested in language learning too so I will submit it at some point :)

Regarding new extra languages - good question :) Thankfully because of the way the code was written, not a lot of work is needed to support a new language. I went from just 1 language (Russian) to the ones I support now in just 1-2 days worth of work. Having said that, some languages are trickier. For example, Japanese needed more work on how the tokens (words/characters) are parsed and split in the UI (to be honest I'm still not sure about how well it works). Also, not all languages are created equal according to Wiktionary. Some languages have way more Wiktionary entries than others (e.g. Korean has fewer entries than Russian). Also, I use some NLP libs for tokenization and lemmatization which vary in accuracy depending on the language.

The whole idea of the project is to experiment with how much can language learning be automated. Can we enable more people to learn a new language if they do not have access to native speakers or teachers? So automating some parts might need some sacrifices in the quality of the material but quite frankly from my own experience the benefit outweighs the occasional wrong word here and there :)