Question2Answer (Q2A) handles language translation differently from other software like Wordpress, where .mo and .po files are used. Q2A uses PHP files for different languages which have an array of strings that are used throughout the platform.
Here is a general outline of how to create and use a language file in Q2A:
Create a new PHP file for your language. In your case, you created qa-tos-lang-ar.php for Arabic. Make sure the file is in the same directory as the qa-tos-lang-default.php file.
The contents of this file should look like this:
<?php return array( 'register_terms' => 'Your translation here', //... other terms go here );
Replace 'Your translation here' with your actual translation.
Make sure your translation file has the same terms as the default language file.
Finally, Q2A needs to be told to use your new language file. Go to the Q2A admin panel, then click on "General" from the left navigation. Scroll down until you see the section for languages. Choose your new language from the dropdown and save the settings.