How to translate the specific line / text / string / sentence in Handsome Checkout from English to my language?

You can do the translation with Loco Translate.

1. Install “Loco Translate” plugin and activate it.

2. Go to the “Loco Translate” menu item in your WordPress Dashboard.

3. Go to the “Plugins” section and select “WooCommerce Handsome Checkout Pages”.

4. Add new language using the “New Language” link.

5. Choose the language to add from the list.

6. Choose the location should be “Author -> plugins/gb-wc-hcc/lang/…”

6. Translate the strings and don’t forget to save when finished.

P.S. If you need to change a specific line of text, you can then search for this line on the “Editor” screen using the “Filter translations” text field.