Hello,
Sorry for the delay.
This is faulty translation issue.
I bet that if you switch the main site language to english, the error will disappear.
Are you actually using Loco Translate or something like that? Did you modify some translation strings by yourself?
In your case, your issue comes from the following string:
<strong.>Leave empty to use default folder</strong.>:<br/><code.>%s</code.>
I suspect that you are using a translation for that string which does include the %s placeholder.
Your translation must include this placeholder, which will be replaced automatically. If the %s placeholder is not included in your translation, PHP will just throw a Fatal Error.
Regards.