I've been in Prague, because my lovely parents took me (and my sister) there for my 30th birthday. It was beautiful and interesting and relaxing (though also tiring because there are a lot of steps and hills).
When I go to other countries where they speak not-English I generally try to learn a few phrases so as not to be a total rudeperson. This goes down well in France, where they either don't speak English that well or just generally prefer it if you speak French (can't blame them) and luckily my French is passable enough that that works OK. In other countries they seem to have decided it's just easier if we all speak English and it's quite hard to get them to talk not-English to you.
In Amsterdam, they can spot an English person at twenty paces and get in their English greeting before you even have a chance to say 'hallo' (which is basically English anyway, because a lot of Dutch is English with a funny accent). In Prague they aren't quite as sure, because you might be Italian or Spanish or French or German instead, so they're sometimes a bit more tentative with the English opener, so you do have a chance to go in with the Czech (and from your poor pronunciation they obviously realise that you're English).
There's a different type of problem though. In Amsterdam, I quite happily parallel-talked, doing my best Dutch beer-ordering and thanking, and they replied in English so that I could actually understand. This worked quite well. But in Prague, it didn't go so well. If I tried to thank them in Czech, they didn't always seem to understand. This is partly because three phrasebooks gave me three different ways of saying it, so I wasn't quite as sure of myself. I'd specifically learnt some phrases, and discovered that my ten weeks of basic Russian would be quite handy (I successfully rustled up the words for 'four tickets').
But I think the biggest problem is that they're making it up. Those three ways of saying thank you, for instance. And look at these signs. They all show what appear to be the words 'from' and 'to' (the first one may not, but the second two definitely do), and there are THREE different ones. The second two, especially, are a dead giveaway that they're making it up, because they're saying the exact same thing. There's no way a difference in the length of time you're allowed to park changes what preposition you use with the times you're allowed to park between.
Reminds me of Welsh, which is definitely doing a similar thing. On one weekend visit not long ago I counted at least three different way of writing 'car park' on signs in just Pembroke Dock.
[08/08/12 Update! 366daysinthelife has informed me that Po - Pa and Po - Ne mean Mon-Fri and Mon-Sun. Of course! It's so obvious once you know. Come back Czech, all is forgiven.]