The alt-right isn't a strictly American phenomenon. France has those too. Marine Le Pen anyone?
At that point Alt-Right just becomes a catch-all term. Although that's how most people on RE use it anyway.
Front National has a really ugly past, but has shifted to a less extreme postion under Marine Le Pen. Now, people might say this is just a tactic to get wider support, and that maybe right, but as far as actual policies go, it isn't nearly as extreme as the party once was. That's not to say it isn't a worrying sign, it is, but last time I checked, they didn't really support a white ethno state, for example.
The point being, the reason for much higher support of Front National perhps isn't because a large section of the French public have turned into raving White Supremacists, it's because they feel the other mainstream parties are ineffective when dealing with immigration. France has been hit with a wave of Islamic terrorism in recent years, as you all know. This has led to greater support of Front National.
Interestingly, this has also led to a change in rhetoric from the more centre parties. They have moved further to the right in a bid to ward off further gain by Front National. The problem is, a change in rhetoric doesn't necessarily mean a change in action. That is likely to be the result when it comes from the Established parties. No change in action might mean the public and the politicians no longer see eye to eye on this matter again.
You know, things like this are important to get right when trying to deal with these issues. Looking at these things and proclaiming they are all essentially the same thing will mean 1) you are ineffective in dealing with it, and 2) you will lose a large section of the public through alienating them.
