The flag power supports over 180 flags.
To make the xat flag use (flag) or (flag#)
To make a country flag use (flag#wus) for the usa flag - animated
To make a still flag use (flag#w1us)
Flags have the following format: (flag#wISO A2 country code)
If you're unaware what A2 code your country has, see here and search (ctrl + f) for your country.
Be advised that this format is not consistent and some flags have the full name of the country, so you might want to try both.