Herein resides translation files for Plate.
A function in functions.php identifies the LOCALE (e.g. da_DK) of your WordPress installation. If there is a language-file in languages/ named accordingly (e.g. da_DK.mo), Plate will use it. Fallback is English.
1 Make a copy of default.po an change the filename to your LOCALE.po (e.g. da_DK.mo)
2 Use poedit to edit your po-file.
3 When saving your po-file, poedit will create/update a corresponding mo-file.
4 Please commit both your po- and mo-file.
http://codex.wordpress.org/I18n_for_WordPress_Developers
http://www.wdmac.com/how-to-create-a-po-language-translation#more-631