I wasn't intending to be arrogant, although yeah I guess it does come off that way. I need to stop posting first thing in the morning.
I'm not saying that any one language is better than any other, but this forum is english-based and so it's implied that by posting here you can read, understand and communicate in the english language. If someone doesn't want to use english then there are plenty of forums available on the Great Big Internet that cater to polish, french, spanish, german, etc. speakers.
If people just go around posting in whatever language they feel like then, as you say, not everyone is going to be able to understand every post and that is undesirable as it reduces readability of the forum. Using multiple languages in one post just makes it more cluttered with redundant/unparsable information. Just as you wouldn't (shouldn't) appreciate it if I decided to increase the length of all my posts by having a copy of them in ASCII hex pairs