I can see that some companies might not want to provide a +800 (00 800) number for free calls, and they're not supported by all telcos, either.
It might be useful to know that you can always dial a certain number to reach, say, your bank or for a big company's customer services to have one number, wherever you are in Europe. Certainly I can imagine being able to advertise 0xxxx abc SONY, for instance, would be appealing to pan-european firms.
You could easily determine the most likely language to answer in by knowing the originating caller ID, and allow people to press a button (ideally a common one) for a language menu if necessary.
The bigger problem, perhaps, is finding a number range that would allow it, in each country - I think that's the only reason you'd want to do this; if you used +800 or had one of the other international codes like +801 allocated, you'd still have pretty long numbers - five digits used up before you even got to allocating digits to subscribers.
Really, if you were to do something like this, you'd want something that's only a digit or two more than national dialling, at most, I'd have thought.