If you want to add new language to the OGP this can be done by creating
new directory with the language name. This directory then contains the 
language files like shown below:

lang/<NEW_LANG>/
lang/<NEW_LANG>/global.php
lang/<NEW_LANG>/modules/
lang/<NEW_LANG>/modules/<MODULE_NAME>.php

All .php files that are in the main directory of language are loaded 
on every page load. The files under modules directory are loaded only
when the specific module is loaded. Check module names from modules/ 
directory.

If you want to check which translations are missing from your language
check the lang/lang-check.php with your browser.