Hi Jakub,
you can use Loco translate, here is the link https://wordpress.org/plugins/loco-translate/ , to change the labels.

Yes every string in the plugin is translation ready. That means you can use tools such as Loco Translate (yes I know you don’t want to translate but change the labels) to get it done. Here’s a quick tutorial https://localise.biz/wordpress/plugin/beginners

I have a quesiton related to the translation of table for this variation of discount. Would it be possible to change labels:

“Quantity based pricing table”
“Unit price”

to the local language by adding snippet of code or custom css?