import re


def human_readable_key(key, delimiter=":"):
    """
    >>> human_readable_key("participants:0:name")
    'Participant 1 Name'
    >>> human_readable_key("participants_hello_world:0:name")
    'Participants Hello World 1 Name'
    """
    """Makes a delimited key human-readable."""
    key = key.replace("_", " ")
    delimiter = re.escape(delimiter)
    key = re.sub(r's?{0}(\d+){0}?'.format(delimiter), lambda x: " " + str(int(x.group(1)) + 1) + " ", key)
    key = re.sub(delimiter, ": ", key)
    key = key.title()
    return key