Download as PDF doesn't work with other than iso-8859-1 characters in title
Examples:
1 https://en.wikipedia.org/wiki/Bohumil_Ku%C4%8Dera
https://en.wikipedia.org/w/index.php?title=Special:DownloadAsPdf&page=Bohumil_Ku%C4%8Dera&action=show-download-screen
https://en.wikipedia.org/api/rest_v1/page/pdf/Bohumil_Ku%C4%8Dera
2 https://en.wikipedia.org/wiki/1909%E2%80%9310_St_Helens_RLFC_season
https://en.wikipedia.org/w/index.php?title=Special:DownloadAsPdf&page=1909%E2%80%9310_St_Helens_RLFC_season&action=show-download-screen
https://en.wikipedia.org/api/rest_v1/page/pdf/1909%E2%80%9310_St_Helens_RLFC_season
Working example: https://en.wikipedia.org/wiki/V%C3%A1rasz%C3%B3