Going more to Europe these days and had some trouble filing flightplans and finding the correct route/waypoints to file. Got a tip from a guy in Le Bourget, he was able to check on the Eurocontrol (or related) website which routes were filed before by other crew and had be accepted.
I am aware of the US version
FltPlan.com Flight Planning & Flight Tracking for General Aviation. which gives you routes that are already filed and usually will get accepted and can be expected.
So far I have found a route validator on the website of Eurocontrol, anyone aware of another way of finding routes that will get accepted?