Accessor: adjust TranslatedPropertyGetter to use unicode2str

partially revert a17bb910 (py2/py3: Make Products code compatible
with both python2 and python3., 2022-04-13) so that
TranslatedPropertyGetter keeps returning utf-8 encoded str (bytes) on
python2 and returns text only on python3.

This regression caused displaying categories to raise unicode error or
to silently not display the labels for.