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/ar_AR/LC_MESSAGES/thonny.po:710: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/el_GR/LC_MESSAGES/thonny.po:717: 'msgid' and 'msgstr' entries do not both end with '\n'
thonny/locale/el_GR/LC_MESSAGES/thonny.po:801: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 2 fatal errors
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/fi_FI/LC_MESSAGES/thonny.po:1454: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/hu_HU/LC_MESSAGES/thonny.po:1450: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/hy_AM/LC_MESSAGES/thonny.po:1607: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/ko_KR/LC_MESSAGES/thonny.po:1456: '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:882: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:887: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:1037: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nb_NO/LC_MESSAGES/thonny.po:1224: '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:882: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:887: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:1037: 'msgid' and 'msgstr' entries do not both begin with '\n'
thonny/locale/nn_NO/LC_MESSAGES/thonny.po:1224: 'msgid' and 'msgstr' entries do not both begin with '\n'
msgfmt: found 7 fatal errors
gettext: thonny/locale/pl_PL/LC_MESSAGES/thonny.po:1192: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/sq_AL/LC_MESSAGES/thonny.po:1467: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/ta_IN/LC_MESSAGES/thonny.po:1465: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/th_TH/LC_MESSAGES/thonny.po:1468: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/tr_TR/LC_MESSAGES/thonny.po:95: 'msgid' and 'msgstr' entries do not both end with '\n'
msgfmt: found 1 fatal error
gettext: thonny/locale/zh_Hans/LC_MESSAGES/thonny.po: can't guess language
gettext: thonny/locale/zh_TW/LC_MESSAGES/thonny.po:1188: '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.