The books are very Britain-centric. Do we have any information about Voldemort being considered a threat outside of Great Britain? Was he know in magic (non-Britain) world or maybe casual non-Britaing mage knew nothing about him?
Edit: question is not about "first Wizarding War being an international event", as it is question about things that happend (or not). Question is more about knowledge of non-Britain mages about Voldemort and fear than can come from it.
There is no concrete evidence, but there are several facts that add up to the conclusion that he is known outside Britain:
Possibly the most unreliable conjecture: we know that Grindelwald, who was German, was known throughout Britain (several books), Bulgaria (Viktor Krum, Harry Potter and the Deathly Hallows) and America (Fantastic Beasts film). So it is fairly safe to assume that a Wizard who is more powerful than him and just as feared would be internationally known as well.
Foreign wizards know about Harry Potter: Harry is recognised by foreign wizards in the Quidditch World Cup (by the Bulgarian Minister for Magic) and the Durmstrang students, both sources Harry Potter and the Goblet of Fire. though this might be because he's the only wizard to have survived the killing curse, it is likely anyone who herd about it also herd about who tried to kill him.
Voldemort does travel: we know that he lived in exile in a forest in Albania and he travelled to and murdered people in Germany. Before he became a famous murderer he travelled the world learning dark magic and practices (Harry Potter and the Half-Blood Prince).
While talking about his trip to Germany, it's also worth noting that Grindelwald, who was in prison since Voldemort's first rise to power knew who the Dark Lord was. And if he knew, locked up with (I'm guessing) not many visitors, then it's fairly safe to say that others, with regular access to new outlets, would know him as well.
When Ron disguises himself as a 'foreign wizard' to accompany Bellatrix-Hermione to Gringotts, Travers is not surprised that a wizard from a non-British country is curious about Voldemort (though he does seem somewhat xenophobic).
Hermione mentions that Harry is in several books including "The Rise and Fall of the Dark Arts" and other such literature, it can again be assumed that Voldemort is mentioned and any anthologies of powerful dark wizards around the world would include mention of the Dark Lord.
I think it's safe to say that a killer with the power and scope that Voldemort possesses would be internationally known, one man working outside the law and being responsible for hundreds (if not thousands) of deaths cannot be swept under the rug. Also let's not forget what he was doing: terrifically breaking the international statute of secrecy, attempting to eradicate muggle-borns, muggle mass-killings, working with Dementors, Werewolves, Giants and other creatures generally considered to be dangerous.
All in all there is not much solid evidence, however adding up the facts it is quite unbelievable to believe that he was unknown globally.
From memory they do mention he is - I think in the Order of the pheonix when hagrid gets back from the giants which were abroad - he mentions something about vodemort drumming up support around the
