Hi Mike!
This plugin handles two kind of texts (like other softwares).
The one kind is the fix texts of the plugin, this is contained by the program code. These texts can be translated using the .po files. You can freely do it, so you can translate this plugin.
The other kind of text is the content that you as the user of the plugin enter. Normally you can use your own language, so this contents also can be “translated”. The tab labels and content belongs to this group.
WPML is another question. WPML has a specific functionality that ensures using more languages in the same system. This plugin is not explicitly prepared for WPML, so you cannot use it with WPML.
As a workaround for using this plugin in multilingual environment, you can use WP multisite with MultilingualPress plugin (https://wordpress.org/plugins/multilingual-press/). But it is a very different way of multi language handling than WPML, so it may not be right for you.
So you can translate this plugin, you can use it for multilingual purposes, but unfortunately at this moment WPML is not supported.
Best Regards,
Peter Rath
WebshopLogic