How to use the extruct.rdflibxml.extras.httpheader.language_tag function in extruct

"""Parses the Accept-Language header.

    Returns a list of tuples, each like:

        (language_tag, qvalue, accept_parameters)

    """
    alist, k = parse_qvalue_accept_list( header_value)
    if k < len(header_value):
        raise ParseError('Accept-Language header is invalid',header_value,k)

    langlist = []
    for token, langparms, q, acptparms in alist:
        if langparms:
            raise ParseError('Language tag may not have any parameters',header_value,0)
        lang = language_tag( token )
        langlist.append( (lang, q, acptparms) )

    return langlist

for langtag, qvalue, aargs in accept_list:
            if len(langtag) >= 2:
                for suptag in langtag.all_superiors( include_wildcard=False ):
                    if suptag not in all_tags:
                        # Add in superior at half the qvalue
                        to_add.append( (suptag, qvalue / 2, '') )
                        all_tags.append( suptag )
        accept_list.extend( to_add )

    # Convert server_languages to a list of language_tags
    if _is_string(server_languages):
        server_languages = [language_tag(server_languages)]
    elif isinstance(server_languages, language_tag):
        server_languages = [server_languages]
    else:
        server_languages = [language_tag(lang) for lang in server_languages]

    # Select the best one
    best = None  # tuple (langtag, qvalue, matchlen)
    
    for langtag, qvalue, aargs in accept_list:
        # aargs is ignored for Accept-Language
        if qvalue <= 0:
            continue # UA doesn't accept this language

        if ignore_wildcard and langtag.is_universal_wildcard():
            continue  # "*" being ignored

        for svrlang in server_languages:
            # The best match is determined first by the quality factor,
            # and then by the most specific match.

accept_list.sort()
    all_tags = [a[0] for a in accept_list]
    if assume_superiors:
        to_add = []
        for langtag, qvalue, aargs in accept_list:
            if len(langtag) >= 2:
                for suptag in langtag.all_superiors( include_wildcard=False ):
                    if suptag not in all_tags:
                        # Add in superior at half the qvalue
                        to_add.append( (suptag, qvalue / 2, '') )
                        all_tags.append( suptag )
        accept_list.extend( to_add )

    # Convert server_languages to a list of language_tags
    if _is_string(server_languages):
        server_languages = [language_tag(server_languages)]
    elif isinstance(server_languages, language_tag):
        server_languages = [server_languages]
    else:
        server_languages = [language_tag(lang) for lang in server_languages]

    # Select the best one
    best = None  # tuple (langtag, qvalue, matchlen)
    
    for langtag, qvalue, aargs in accept_list:
        # aargs is ignored for Accept-Language
        if qvalue <= 0:
            continue # UA doesn't accept this language

        if ignore_wildcard and langtag.is_universal_wildcard():
            continue  # "*" being ignored

all_tags = [a[0] for a in accept_list]
    if assume_superiors:
        to_add = []
        for langtag, qvalue, aargs in accept_list:
            if len(langtag) >= 2:
                for suptag in langtag.all_superiors( include_wildcard=False ):
                    if suptag not in all_tags:
                        # Add in superior at half the qvalue
                        to_add.append( (suptag, qvalue / 2, '') )
                        all_tags.append( suptag )
        accept_list.extend( to_add )

    # Convert server_languages to a list of language_tags
    if _is_string(server_languages):
        server_languages = [language_tag(server_languages)]
    elif isinstance(server_languages, language_tag):
        server_languages = [server_languages]
    else:
        server_languages = [language_tag(lang) for lang in server_languages]

    # Select the best one
    best = None  # tuple (langtag, qvalue, matchlen)
    
    for langtag, qvalue, aargs in accept_list:
        # aargs is ignored for Accept-Language
        if qvalue <= 0:
            continue # UA doesn't accept this language

        if ignore_wildcard and langtag.is_universal_wildcard():
            continue  # "*" being ignored

        for svrlang in server_languages: