Go to Loco Translate > plugins > Pacz Custom Post > Advance settings > Should be same in attached image.
Then click on overview > Click on +New languages > Add here new language, Your language should be same like as site language of the theme as in attached image.
Then again Click on Overview and select 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.
when theme will be update you will go to loco translate > plugins > select plugin (depend on translation) > Edit language > and click on sync button as in attached image so you can see all new words that’s will be came or include in updated theme.
Hope this Article will help you