languageExclusion = '-' LANGTAG STEM_MARK?

def _language_exclusions(stem: LanguageStemRange,
                             exclusions: List[ShExDocParser.LanguageExclusionContext]) -> None:
        """ languageExclusion = '-' LANGTAG STEM_MARK?"""
        for excl in exclusions:
            excl_langtag = LANGTAG(excl.LANGTAG().getText()[1:])
            stem.exclusions.append(LanguageStem(excl_langtag) if excl.STEM_MARK() else excl_langtag)