If you use Loco to change one string in your standard language file, you will create a custom language. If you save this language file in the normal location, it will be overwritten the next time Woo update the plugin. If you save it in the custom location, it will be protected from being overwritten, but you will need to update it yourself whenever Woo bring out new strings. This would be a burden. The Loco documentation explains the custom location.
Instead you can use the Say What? plugin:
https://www.ads-software.com/plugins/say-what/
Go to Dashboard > Tools and set up text replacements. The settings would be:
Original string: %s has been added to your cart.
(must be exact, must be the text when English (United States) is the site language)
Domain: woocommerce
Context:
(leave empty)
Replacement string: %s has been put in your basket.
(your choice of words of course. %s is replaced with the number at run time.)
You’ll need a second text replacement for the plural case.
Original string: %s have been added to your cart.
You can do the the same thing with the gettext filter in your child theme’s functions.php, but that would be more effort and of no extra benefit.