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 thonny 's PO files:

gettext: thonny/locale/el_GR/LC_MESSAGES/thonny.po:725: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/es_ES/LC_MESSAGES/thonny.po:307: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/nb_NO/LC_MESSAGES/thonny.po:73: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:428: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:480: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:871: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:876: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:1026: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:1209: 'msgid' and 'msgstr' entries do not both begin with '\n'
msgfmt: found 7 fatal errors
gettext: thonny/locale/nn_NO/LC_MESSAGES/thonny.po:73: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:428: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:480: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:871: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:876: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:1026: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:1209: 'msgid' and 'msgstr' entries do not both begin with '\n'
msgfmt: found 7 fatal errors
gettext: thonny/locale/pl_PL/LC_MESSAGES/thonny.po:1193: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/tr_TR/LC_MESSAGES/thonny.po:87: 'msgid' and 'msgstr' entries do not both end with '\n'
thonny/locale/tr_TR/LC_MESSAGES/thonny.po:1492: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 2 fatal errors
gettext: thonny/locale/zh_Hans/LC_MESSAGES/thonny.po: can't guess language
gettext: thonny/locale/zh_TW/LC_MESSAGES/thonny.po:1189: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
      

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.