What exactly is BJP's Malviya lecturing Mamata on amid Bangla row?

As a letter by the Lodhi Colony Police Station to the Banga Bhawan in Delhi requesting an official to help understand "Bangladeshi language" sparked a political storm, BJP leader Amit Malviya tutored West Bengal CM Mamata Banerjee on Bangla. But what exactly was Malviya, who called Mamata "poorly lettered", trying to explain to the native speaker of Bangla?