After you have successfully gotten the code snippet you need to add it to the checkout page. To do this go to the checkout page located in the settings section of the Shopify admin. Here is a direct link: https://www.shopify.com/admin/settings/checkout
Scroll down to the Order processing section, in the input labelled Additional scripts, paste the Weglot snippet as shown in the below screenshot.
Here is a video showing how you can add the code snippet in the Shopify checkout page. https://www.loom.com/share/eab2ddeea1624bf487a0e15817e53aff After you have successfully added the coding snippet on the Checkout page the Popup will be translated to the language you select.