Increase charset=“utf-8” Font size in php/mysql site

Question

Please see www.favoritebd.com. Here you can see two language (1) Bangla and (2) English. So to enable Bangla Language I used..

header('Content-Type: text/html; charset=utf-8');

Issue is Bangla font size, it's smaller than English fonts. So is there anyway to increase ONLY BANGLA FONT SIZE or can I use css property/value like charset=utf-8'{ font-size:18px;}(I don't know is it valid!)

However in my css i used...

div.font{ font-size:120%; font-weight:normal;}

To increase the Bangla font size but it's also increase English font size but I just want only increase bangla font size.