Pronunciation of "यह"
While Duo claims that "in formal and literary contexts", the pronunciation of यह as "ye" is incorrect, I think it would be helpful for the audio program to still use this pronunciation; from what I've seen, "yaha" (the currently used pronunciation) is rarely used in common speech. I was recently practicing Hindi with some of my Indian relatives, many of whom live in India, and I used the pronunciation "yaha" in a sentence, thinking to be more formal with my elders. Everyone in the room looked at me like I was crazy and no one had any idea what I was saying until I explained myself. None of them had ever even encountered that pronunciation!
For practicality, then, I think it would be best if Duo could settle on "ye"; we can always keep the pronunciation of "yaha" in the back of our minds, but, from what I've seen, it's unlikely that we'll ever really use it.
Technically correct grammar is less important that everyday comprehensibility.
I too take issue with the claim that the usual pronunciation of यह and वह as ye and vo is incorrect. The non-phonetic pronunciation of certain words containing ह (महल, बहन etc) is a feature of Hindi (bar a few dialects). Saying it is incorrect would be like saying Schwa-deletion, which is also a feature present in Hindi but not in Sanskrit, is 'colloquial' and incorrect (For example, If you pronounce आसमान (sky) as 'āsamāna' instead of 'āsmān', I am pretty sure absolutely no Hindi speaker would understand what you are saying).
And I agree, but my point was about the progression of study. Everybody in our school learns 'yaha' and uses it too throughout school for writing. Especially if language chosen in 9th standard is hindi . You cannot write 'ye' in Board exams, they deduce marks for that. And I agree with you completely on usage, my argument was to defend the reason for learning 'yaha' though it should be taught which is more commonly used. Regards.
You learn it wrong in schools, for the sake of OCD-afflicted pandits who are not teaching to educate, rather teaching to enforce order and control. No one learns that in Pakistan, when they are speaking the same language ("Urdu"). It's almost purely a modern [Sanskrit-centered] school convention of no value to anyone learning the language.