Problem:
I'm trying to translate the button "add to cart" in WooCommerce single product page. But can't find this in the strings menu or anywhere.
Solution:
Go to WPML → String Translation area, check the Look for strings while pages are rendered option at the bottom of the page, refresh the page where the add to cart text is visible, go back and uncheck the Look for strings while pages are rendered option, and search again for the string in WPML → String Translation.