How to add new language in osCommerce template ?

1. At first check how many languages follow your template. 
2. Then go to yourdomain.com/admin/login.php and use your username and password to log in.
3. Click Tools in left menu and then version checker.
4. Ignore last two numbers of version. It can be something like: 2.304. This means your version is 2.3.
5. Now go to addons.oscommerce.com
6. Search your language here and check that it's exactly the same version as your template.
7. Download it. Then go to yourdomain.com:2082 and login with your FTP user and password.
8. Click file manager and go to main directory.
9. Click upload and select language package.
10. After it's done click Extract which will extract language files to FTP. 
12. When it's done get back to oscommerce admin panel.
13. Click New language. 
14. Fill out the fields. Note that directory name is the same as two letter name. For example for Russian is 'ru'.
15. When you're done filling out click Save.
16. Done. Changes will be affected after you visit your osCommerce website again.