You could just as well say 1922 because the Ottomans also claimed to be the successor to the Roman Empire, or alternatively 1917, because the Russian Empire did too.
The more realistic alternatives are 'around 480', 1204 or 1453 :)
Voltaire gets quoted so often without ever mentioning that the German word "Reich" has a different meaning than the loose translation "empire". A "Reich" is not necessarily an empire, so no news here.
It's true that the "Heiliges Römisches Reich" (literal translation "Holy Roman Realm") considered itself the successor of the Roman Republic. The English referred to the Roman Republic by what it was in the modern sense: an empire. Therefore its self-proclaimed successor got translated as "Holy Roman Empire", which, unlike the original, it is not.
Almost every single statement in this sentence was wrong. It was founded as the Sacrum Imperium -- literally the Holy Empire. "Heiliges Römisches Reich" was a later German translation of the Latin term for it. Charlemagne explicitly had himself crowned as the emperor. It was never in any sense a republic and it never pretended to be.
In the Latin phrasing, which they likely used, the word "Imperium" appears. Good point. Still, the original meaning of "Imperium" was slightly different than what it is today. So my point goes more like this: The Germans didn't claim to found an empire in the modern sense, so it's not that surprising that Voltaire pointed out, it isn't one.
Fair point, the original sentence is French and not English. Both are closer to Latin than German, so the mistranslation might be more on the German side.
That claim rests on their being the successor to another state (the Ottoman Empire) whose claim rests on the right of conquest. “Roman Emperor” was one of the titles of the Ottoman sultans and it received some recognition from both their subjects (who continued to call themselves “Roman” for centuries) and other states.
The more realistic alternatives are 'around 480', 1204 or 1453 :)