I took the North Sea Cycle Route in the other direction (from Paris to Amsterdam) last year. One thing that surprised me is that it contains just about every hill in all of Holland. The route follows the shore of the North Sea, so you spend a lot of time going up and down sand dunes. It's really pretty and there will be lots of other cyclists out there. It's also one of the places where you'll find plenty of campgrounds.
If you plan to go that route, consider getting the official map and guide book of the LF1 cycle route. It shows the locations of campgrounds, hostels and cafes along the route. It also shows the route in detail, although the map doesn't show much of anything away from the official route. Even though it's supposed to be well signed, I found that there were quite a few critical junctions that either were not signed at all, or where the sign was after the turn. The map made it possible to find my way back.
As for language issues, I didn't speak a word of Flemish or Dutch, but everyone in Holland and Belgium was very accommodating. I do speak a little tortured Canadian grade-school French. It was enough to get by in northern France, with a little help from the locals. I think they just appreciated the effort.