'Returns True if the given lang has been registered and
is a Citadel-based language.
A "Citadel-based" language is one that uses CIX/CIDB/CITDL tech for
its codeintel. Note that currently not all Citadel-based langs use
the Citadel system for completion (e.g. Tcl).'

def is_citadel_lang(self, lang):

    return (lang in self._is_citadel_from_lang)
