I think there are some missing commas in the example. Probably just a typo, or perhaps the author thought they'd used too many already. It's a horribly long sentence - a terrible example of English legalese, and it is on the verge of being almost impenetrable.
Here are some extra commas to help break it up a bit into digestible pieces.
Either the issuer's place of business, where the undertaking is
issued, is located in a country that has adopted the Convention, or
under international conflict of law principles, the law applicable to
the undertaking is the law of a country that has adopted the
I've read it several times over. Still makes hardly any sense to me, but then I'm not a lawyer, just a simple human;)