Return a text description of a PhoneNumber for the given language.

    Arguments:
    data -- Prefix dictionary to lookup up number in.
    longest_prefix -- Length of the longest key in data.
    numobj -- The PhoneNumber object for which we want to get a text description.
    lang -- A 2-letter lowercase ISO 639-1 language code for the language in
                  which the description should be returned (e.g. "en")
    script -- A 4-letter titlecase (first letter uppercase, rest lowercase)
                  ISO script code as defined in ISO 15924, separated by an
                  underscore (e.g. "Hant")
    region --  A 2-letter uppercase ISO 3166-1 country code (e.g. "GB")

    Returns a text description in the given language code, for the given phone
    number's area, or an empty string if no description is available.

def _prefix_description_for_number(data, longest_prefix, numobj, lang, script=None, region=None):
    """Return a text description of a PhoneNumber for the given language.

    Arguments:
    data -- Prefix dictionary to lookup up number in.
    longest_prefix -- Length of the longest key in data.
    numobj -- The PhoneNumber object for which we want to get a text description.
    lang -- A 2-letter lowercase ISO 639-1 language code for the language in
                  which the description should be returned (e.g. "en")
    script -- A 4-letter titlecase (first letter uppercase, rest lowercase)
                  ISO script code as defined in ISO 15924, separated by an
                  underscore (e.g. "Hant")
    region --  A 2-letter uppercase ISO 3166-1 country code (e.g. "GB")

    Returns a text description in the given language code, for the given phone
    number's area, or an empty string if no description is available."""
    e164_num = format_number(numobj, PhoneNumberFormat.E164)
    if not e164_num.startswith(U_PLUS):  # pragma no cover
        # Can only hit this arm if there's an internal error in the rest of
        # the library
        raise Exception("Expect E164 number to start with +")
    for prefix_len in range(longest_prefix, 0, -1):
        prefix = e164_num[1:(1 + prefix_len)]
        if prefix in data:
            # This prefix is present in the geocoding data, as a dictionary
            # mapping language info to location name.
            name = _find_lang(data[prefix], lang, script, region)
            if name is not None:
                return name
            else:
                return U_EMPTY_STRING
    return U_EMPTY_STRING