on CPAN I found Country. This might help.It has a country object which you could use. If you are successfull to create the object you have a valid country.
Dont know how your data is arranged so getting a single country out of a sentence might be a problem. However you could try to check only on words which begin with a uppercase (in case your countrys are correctly spelled)

Havent tried that though.

Cheers
Schuk