Go to Loco Translate > plugins > Pacz Custom Post > Advance settings > Should be the same in the attached image.
Then click on overview > Click on +New languages > Add here new language, Your language should be the same as site language of the theme as in the attached image.
Site Language
Then again Click on Overview and select a new language that’s you have been make as in attached image.
And now you can translate the words that’s you want to translate e.g ” ADD TO CART ” word.
Important Note:
When the theme will be update you will go to loco translate > plugins > select plugin (depend on the translation) > Edit language > and click on sync button as in the attached image so you can see all new words that’s will become or include in updated theme.
Hope this Article will help you