Arguably the most important VoIP solution that can be localised. This Skype devzone article shows the importance of localisation – ony 28% of users of Skype make use of an English interface.
Skype makes use of Qt Qt .ts files for localisation. Thus a compiled Qt .qm file should bring localisation to your Skype GUI. Unfortunately, certainly on the Linux builds, Skype does not seem to detect languages based on the presence of a language file, rather it seems to have a pre-set list of possible interface languages. Rather sad as this would have been an easy GUI to localise based on the power or Qt.
It is possible to update languages that exist within the Skype application. This thread (in Hungarian) links to Hungarian .ts and .qm files. In a Fedora install these are missing and by adding the files Hungarian becomes an available interface languages. This does not work though for Afrikaans (even if the files are renamed), which seems to indicate that the supported languages are pre-set within the binary.