You are able to translate plugin using mo files. Plugin is fully compatible with WPML.
If you want to use plugin with WPML you should enter all strings in English, no matter which language you’ve set as default. All book’s custom fields and texts should be translated via WPML String Translation.
In case you don’t want to use WPML and you simply like to translate your plugin in one single language visit F.A.Q. section to see several ways to do it.