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 pydata-sphinx-theme 's PO files:

gettext: src/pydata_sphinx_theme/locale/ca/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/cs/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/en/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/es/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/fr/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/it/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
gettext: src/pydata_sphinx_theme/locale/ru/LC_MESSAGES/sphinx.po: warning: Charset missing in header.
                                                                                                                             Message conversion to user's charset will not work.
      

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.