rilwis/meta-box — pull request #475 by mirozoo (2014-08-25 16:37:17+00:00)
Title: jQuery UI Datepicker/Timepicker locale files...

...aren't being loaded if the WP locale definition doesn't match the corresponding value in the filename (e.g. "de-DE" vs. "de"). Checking the alternate filename variants (e.g. jquery-jquery-ui-timepicker-de.js instead of ui-timepicker-de-DE.js) did the trick for me.