Hello!
The only person that I imagine it is, is our teacher!!
Because: how can someone know that Dobri Den is Polish?! She is the only one who knows that. Anyway she could do that propositally (does that word exist?). She was the only one that knew that in Polish it's dzien dobry and not Dobri Den.
And there's another thing. Wasn't this blog made only for the students of 2nde? The teacher is the only one who can add more or fewer writers to this blog. I don't think she would let someone from outside to write on this blog. She probably made up that name and wrote what she wanted.
All the mistakes could have been made propositally!!!
Teacher, I think it's you!