Because I keep finding bugs where translation is impossible due to missing tra(), tr() or tr in curly braces, I opened this new umbrella bug report.
Here I will add only newly found bugs, I will not integrate the already existing bug reports into this!
/lib/prefs/calendar.php has this on line 78:
'description' => 'Interval to show between minutes on time selectors',
Without tra(), the description cannot be translated into any language...