Easy installation through OpenCart Installer
Go to Extensions >> Installer and press the Upload button.
Find the zip file in your computer and upload it to your OpenCart.

Go to System >> Localisation >> Languages and press the Add New button.
Enter the following values in the text fields, or choose from the select menus:

Language Name: Romanian
Code: ro-ro
Locale: ro_RO.UTF-8,ro_RO,ro-ro,romanian
Status: Enabled / Disabled
Sort Order: 0 (if you want Romanian language to be listed as the first language)