Planescape the words were real if antiquated lower class English slang that even someone not particularly versed in that culture with a decent grasp of English can gather the meaning of through logical inference. Somewhat in the manner of Gene Wolfe. It added colour and feel to characters who spoke like that and differentiated them from characters who spoke formally or in today's English.
Some of those terms in the dictionary above are still regularly used in my culture (especially by older generations). Watch Mad Max 1 for instance and some of the characters have a similar style of speaking.
I'm not sure that this is always down to how English it is. First, we have quite a few people who speak other languages, even in the Codex, that seem to have found POE-speak annoying. Second, we are apparently fine with
more exotic pseudobabble, like "Tasloi" or "Sahuagin", or with faux-Greek/Latin. So I suspect a lot of it is down to pop culture exposure and what people think wizards and dragons are "supposed" to sound like.
E.g. if someone asked me whether to go with Sigilspeak-style or POE faux-Italian style in a game, I'd go with the former, purely because even as a non-Brit, I'll generally have more cultural references to know what all these words are supposed to feel like.
Funnily enough, my personal 'worsts' are bad not because they're not English (why would anyone give a fuck?) but because they often cut too close to what they were referencing: "Knight-Captain" in NWN2 is just some amazing 13 year old power fantasy energy, while I have of course whined many times about god damn Bleden Mark.