For several releases now Ubuntu comes with incomplete language support out of the box. This is done in order to save space on the CD media so other more important components can fit in the limited room. Once the system is installed if we go to "System > Administration > Language Support", Ubuntu will ask us to install the full language support. At this point the installation can fail showing a message that we have broken packages. In order to fix this we need to:In my particular case I had Thunderbird installed from PPA. One of the packages from language support was thunderbird-locale-en_gb which was not in the PPA but in Ubuntu's repo and it depended on the Thunderbird from Ubuntu. That made it "non-installable".
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