I don't understand much about translation object files, but it seems to me that this file: /usr/share/locale-langpack/en_GB/LC_MESSAGES/gwibber.mo doesn't contain a translation for 'authorised'.
I don't understand much about translation object files, but it seems to me that this file: locale- langpack/ en_GB/LC_ MESSAGES/ gwibber. mo
/usr/share/
doesn't contain a translation for 'authorised'.