Apple changed the default Bangla font to Kohinoor Bangla on El Capitan. However, you can bring back the old font (BanglaSangamMN) in Safari very easily.
- Click Here to download the necessary files. Put user-style.css along with other files in a folder.
- Then open Safari & go to Preferences > Advanced.
- Now click on the dropdown box beside Style sheet
- Click Other, Then browse & choose user-style.css.