When logging in on Google Webmaster Tools for an unrelated task, i noticed these message:
Fix mobile usability issues found on http://zh-min-nan.wiktionary.org/
Fix mobile usability issues found on http://zh-min-nan.wikiquote.org/
475
Pages with errors
"Viewport not configured"
"Small font size"
"Touch elements too close"
"Content not sized to viewport"
At a glance it looked like this is only popping up for zh-min-nan non-WP projects, so maybe MobileFrontend is not enabled there or something?