Julie here from Shopify Support.
There is a section for Checkout & system in the language editor, which allows you to edit the wording that appears in your checkout. If you deleted wording in one of the fields there, then the best way to replace it would be to install a fresh version of your theme. You don't need to publish this theme; instead, you can use this theme to access the language editor and see what was entered in the Description html field so you can then add it back to your currently published theme.
That being said, I took a look at the language editor for my own theme (I'm currently using Brooklyn) to see what's entered in the Description html field and this is what I see:
However, this may be a bit different on your end, depending on the theme you're using. For that reason, it might be a good idea to install a fresh version so you can confirm if this is the case.
I hope this helps! Let me know how that goes.