Quote Originally Posted by Valda View Post
My Russian isn't that good yet (yet is indicating that it's a work-in-process and that it's likely to get better)
My Russian is still isn't that good yet ("I know you've expected my Russian to be better, but it's still not that good)
'My Russian *is* still isn't that good yet' -> That's incorrect. Omit the 'is.'

Quote Originally Posted by The Doctor View Post
Ага, тогда имеет ли какой нибудь смысл фраза: I'm still here yet. (я хочу сказать "Я еще здесь", используя слово yet.
Или если есть слово "still", то уже нельзя употреблять "yet"?
"I'm still here, yet I needed to leave an hour ago."

The above sentence expresses your current situation (present) but don't be confused with saying 'needed' (you might think that refers to some actual past event). It's merely stating it *should* have been a past event (according to the narrator).

'Yet' in this context is the same as using the word 'nevertheless.'

Using yet and still