Yes, you can easily translate our plugin into your own custom language via loco translate plugin. You can check the documentation here .
We haven’t checked our WCMp PDF Invoice plugin under multi lingual settings. You can use any translate plugin such as loco or WPML to translate the plugins. For translation using loco plugin, you can check here.
For this, all you have to do is, sync the strings first (see this screenshot – https://prnt.sc/m57rmn) and then start translating.