Yes, that’s true when the language is used by one country only, or more countries very close to each other. So I guess there are no differences between standard German in Germany compare to standard German in Austria or Switzerland. But English is different. Standard American English is definitely different than British English. So by general English you mean which one? American or British? Because you can’t have some mixture.
I’ve posted there several tongue in cheek examples of English with Czech accent, but now I would like to post one serious example. This one would be probably very close to what we can expect from English with Czech accent in the game. This is clip from low budget American film about Czech history (ridiculous, isn’t it?) called The Pagan Queen. The film itself is disaster, with average rating around 2 of 10. Most of the cast are Czechs, Slovaks, Hungarians and Croats, thus there is no native English speaker at all. In my opinion it sounds really weird. Most of the time it isn’t even Czech accent, it is some strange Eastern Europe mixture. They’re struggling very hard to maintain some level of English, where the English is still understandable for average English user, but at the same time has some “local” elements. There isn’t long dialogue in that YouTube clip, so if you want to explore it deeper, I would recommend you to download the whole film on Pirate Bay. Even if you’re against piracy, because the film is definitely not worth of your money.
But what you’ve written is generally true. Mostly it is thing of education and ability to adapt your tongue to different accent. My point was that nearly every nation has its -----glish version, which is usually the worst version of English you can encounter, not only by accent, but mostly by bending the grammar rules of English toward the native language.