Perhaps the last revision (?), but feel free to refute if I have made any boo-boos:
AFAIK, these are the Countries and Islands (islands prepended with an asterisk) that Twain visited:
AustraliaAustria*AzoresBelgium*BermudaCanadaCzech Republic (or whatever the country of which Prague is a part was then called)EgyptEngland*FijiFranceGermany*GibraltarGreeceHungaryIndiaIrelandItalyLebanon*Madeira*MauritiusMorocco (Tangier)MozambiqueNetherlandsNew ZealandNicaraguaPakistan (then part of India)Palestine (now parts of Israel, too?)Panama?RussiaScotlandSouth AfricaSpainSri Lanka (then known as Ceylon)SwedenSwitzerlandSyriaTasmaniaTurkeyUkraine (then part of Russia; specifically "the Crimea")Wales(not to mention 44 States of the U.S., all but Alaska, South Dakota, Oklahoma, New Mexico, Arizona, Texas, and Alabama)

- B. Clay Shannon