An index page such as https://wikisource.org/wiki/Index:Caba_Executive_Order_No._17_-_2020.pdf results in
Unable to load Wikisource info from 'https://wikisource.org/wiki/Index:Caba_Executive_Order_No._17_-_2020.pdf'
And one with mul., https://mul.wikisource.org/wiki/Index:Caba_Executive_Order_No._17_-_2020.pdf (not that that is what we should expect people to enter) gives
Impossible to access an attribute ("0") on a string variable ("Wikisource 'mul' does not exist").
in templates/base.html.twig:42
The component responsible for this is probably PHP-API-for-Wikisource.