Help to integrate polylang with another plugin

It’s a long shot, but I will try.

I was wondering if there is a “simple way” to get to translate a plugin
(https://ww.wp.xz.cn/support/plugin/woo-conditional-product-fees-for-checkout/) using Polylang and/or this tool below https://ww.wp.xz.cn/plugins/theme-translation-for-polylang/.

What I am looking for, is either to see if I can modify their functions of displaying a text field or if there is some specific procedure I could send to the developers of the plugin in order to make it compatible with Polylang?

Thanks a lot,
Nikolas