Thank you for the login detail.
When we inspected your site, there was this section to translate the string from the customizer as you can in the screen record below:
Also, the changes in the backend are not visible may be because you have set the default language as french. So please once switch back to English and also set the customizer string to default English. Now translate the string from te backend as we display in the record.
Kindly let us know if that works or not?