Post Purchase Upsell Hero displays your offers in your store language and translates all default texts automatically, for example the button labels and the countdown text.
When you create a funnel, all standard texts are pre-filled in your store's language. Default translations are currently available for English, German, Dutch, French, Polish and Spanish, and you can customize every wording on the Translations page. New languages are added via your Shopify Language Settings.
This is the most important rule to understand:
So if you change a wording on the Translations page and nothing happens on your live offer, that is expected. Open the funnel itself and change the text there.
The most common causes:
Use the language preview in the Offer Editor to check your offer in every language your store sells in, and adjust texts where needed. Do this before publishing, and place a test order to verify the live result.