We do know Cirno can read. Whether she knows any English is beyond our knowledge, but she seems quite sure of herself here. Then again, this is Cirno, so who knows if her confidence is well-placed.
She can read it and make it sound like she knows English, just by saying shit: no one will be able to say whether if what she says is true or not.
Teacher...
I don't understand English.Well then, Dai-chan...
Please start reading the English sentences from page 7.EnglishI don't know any either!!If I read now, I'll be the strongest!!