You can check if a PO file is valid with the following command:

        msgfmt -c -o /dev/null <po file>
      

The following errors were found in supertux 's PO files:

gettext: data/levels/bonus4/ko.po: warning: Charset "CHARSET" is not a portable encoding name.
                                                                                   Message conversion to user's charset might not work.
gettext: data/levels/christmas2016/ko.po: warning: Charset "CHARSET" is not a portable encoding name.
                                                                                          Message conversion to user's charset might not work.
gettext: external/tinygettext/test/broken.po: can't guess language
gettext: external/tinygettext/test/level/de.po: warning: Charset "CHARSET" is not a portable encoding name.
                                                                                                Message conversion to user's charset might not work.
gettext: external/tinygettext/test/po/de.po:28:47: invalid multibyte sequence
external/tinygettext/test/po/de.po:72:10: invalid multibyte sequence
external/tinygettext/test/po/de.po:100:18: invalid multibyte sequence
external/tinygettext/test/po/de.po:100:22: invalid multibyte sequence
external/tinygettext/test/po/de.po:148:21: invalid multibyte sequence
external/tinygettext/test/po/de.po:148:36: invalid multibyte sequence
external/tinygettext/test/po/de.po:156:20: invalid multibyte sequence
external/tinygettext/test/po/de.po:164:29: invalid multibyte sequence
external/tinygettext/test/po/de.po:164:30: invalid multibyte sequence
external/tinygettext/test/po/de.po:212:38: invalid multibyte sequence
external/tinygettext/test/po/de.po:216:13: invalid multibyte sequence
external/tinygettext/test/po/de.po:216:37: invalid multibyte sequence
external/tinygettext/test/po/de.po:220:36: invalid multibyte sequence
external/tinygettext/test/po/de.po:228:52: invalid multibyte sequence
external/tinygettext/test/po/de.po:244:55: invalid multibyte sequence
external/tinygettext/test/po/de.po:245:11: invalid multibyte sequence
external/tinygettext/test/po/de.po:265:14: invalid multibyte sequence
external/tinygettext/test/po/de.po:277:10: invalid multibyte sequence
external/tinygettext/test/po/de.po:285:27: invalid multibyte sequence
external/tinygettext/test/po/de.po:289:14: invalid multibyte sequence
msgfmt: too many errors, aborting
      

Please ask the translator (identified by the Last-Translator field in the PO file), the language team (identified by the Language-Team field) or debian-i18n for a fix.