About Extension:Scribunto/Lua_reference_manual. Choosing "Print/Export/ | Download to PDF" url the presented PDF shows this on top:
Language: English • <bdi lang="fr">français</bdi>•<bdi lang="ru">русский</bdi>• ...
That is, tags are visible. It is also present in the downloloaded file. (Does not occur outside the "Language" box, does not occur in "Printable version"). I have FF 25.0 atop WinXP SP2,3; Adobe Reader 7.0. Printscreen available on request; I'm from enwiki.
Topic on Project:Support desk
Could you file a bug with this information?