I'd second Jan's suggestion of going to Belgium. L2K is great, and a nice easy introduction to "going foreign", it's also good for a short day trip. However, as I'm always starting at least a couple of hours from the channel, that tends to make overnight stays a more attractive option.
Personally, I like Ostend or perhaps I should really say Oostende (I've never understood why we think it's okay to change the name of other people's cities or countries). I've been there three times over the last few years, there's nothing much at the airport, you need to get a taxi into town, which is really nice. We tend to coast out round the Thames estuary or East Anglia, depending on where we've stopped for coffee/toilet/crew change. The offshore danger areas seem rarely to be active, but you could go Dover-Calais if you don't like over-water, it doesn't particularly bother me, just carry the right equipment and be as high as possible. ATC have always been spot on and pretty much everyone on frequency seemed to be using English. The airport fees are moderately pricey as I recall, but there's no need for a handling agent
, as the Op's guys give you a lift between parking and terminal.
Or if you want to head the other way, there's the Isle of Man, not very exotic, but just about foreign (technically) and Ireland. No language or ATC issues for either of them, so maybe a good place to start.