How to change the forum language
You're looking the languages in wrong place.
Just change your WordPress to Hebrew and wpForo will load the Hebrew language from PO/MO files automatically. For the translation customization please read the doc: https://wpforo.com/docs/root/translation/how-to-translate/
In case you want to say thank you !)
We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.