But that's not an excuse for foreigners. Those who are not good at the second-language should improve it before they use it.(not only English)

I understand your point, but on the other hand I think the best way to improve language skills is by using it. I know my english isn't perfect and how can it be when it's not my mother tongue? That doesn't necessarly mean that I have nothing to say. I try hard to avoid mistakes by using my dictionary and I often let a friend proofread before I post, but that doesn't cover every little fault. I appreciate the patience I receive from my english speaking friends. If someone isn't willing to accept a few mistakes that can't be wipped out, he should simply ignore the person and be glad to obviously never make mistakes himself.
One life. Live it.