Most people who make these claims probably don't know about the tips and notes sections that come with each earlylesson, where they explain grammar rules and other stuff that will help you along the lesson (for example, here is the tips and notes section for the first Hebrew lesson). In later lessons, when you already have a basic understanding of the grammar, there isn't a tips and notes section anymore, which is a bit of a shame. If there's still stuff you don't understand, though, you can always use the discussion section to ask other users about the questions you have. You're right that you can't learn an entire language just using Duolingo, but you can't learn an entire language from any single resource, class, textbook, or anything else. I think it works best as a supplement to several other resources you're using at the same time to learn a language. It definitely works much better with well-known European languages like Spanish and German, but it's not nearly as bad as you guys are making it out to be.
The one I use on Android from Livio is amazing. It's simple, supports 8 different languages, and it even works offline. I suggest you take a look:
The continuous form is -teiru/-teimasu but I'm not sure how it would work with iku
According to this, it means ‘I'm currently traveling (and hasn't return yet)’
Glad to know that whore, slut, prostitute, B*tch, along with plenty of other words are not gender based. Or carry the (+female) connotation.
I mean there are whole dictionaries and books that explore this issue.
The A-Z of Non-Sexist Language (Women's Press Handbook Series) https://www.amazon.com/dp/0704344300/ref=cm_sw_r_cp_api_glt_fabc_XS0D2A8MPHJ6SMKVWQAN
Language: the Social Mirror (Sociolinguistics) https://www.amazon.com/dp/1424004322/ref=cm_sw_r_cp_api_glt_fabc_QTNT00B8QH3Q07QE0RS4
I'm better acquainted with Proto-Japanese grammar/morphology than Proto-Japonic (mostly because I haven't delved into Ryukyuan studies very deeply), but I suppose I know more than your average joe about it...
Most of what I've learned, I've picked up from Alexander Vovin's Western Old Japanese comparative grammar (revised version forthcoming) and Bjarke Frellesvig's history of Japanese. Vovin and Frellesvig have substantially different ideas on some key points of the proto-reconstructions—like the derivations of some morphemes and the interpretations of some tricky Old Japanese passages—and the two of them together can provide a good breadth of understanding.
I've also got a whole lot of my own thoughts on reconstructions, but the world isn't ready for them yet...
For Lakota, I found a few textbooks on Amazon. I heard this one is very good. It should come with an audio supplement. I actually have a copy of it, but I haven't really used it because I don't really have time to study it.
The issue is, though, that the textbooks do run a bit high ($30-40).
We used this textbook because my professor hated Al-Kitab and renounced it.