def join_strings(strings, level):
    """
    Define join symbol by level and join strings.
    
    :type strings: collections.Iterable[unicode or str]
    :param strings: strings to join
    :type level: int
    :param level: deep level
    
    :rtype: unicode
    :return: joined string
    """

    return (u', ' if level is None else u',').join(strings)