On mobile view with locale= spanish, the navigation tabs change font sizes. See screenshot https://www.dropbox.com/s/qa0d763sd2z3859/Screenshot%202014-10-16%2010.49.39.png?dl=0 It kinda looks awkward.
this is intentional
I showed the fonts to phil before filing the bug and he was unhappy with it.
Then let's just bump up the font size, since that was originally done in part to address nav issues that have been subsequently improved (ngoke) and are getting re-worked (though the rework may not address this particular issue).
Looks good now. At some point the nav was redone and it will be again (slide out shelf is coming). How it looks after fix: http://i.imgur.com/7wCCIH9.png