As a non-native speaker myself (Italian), I too often notice what seem to be patterns in other non-native speaker's English writing that seem to be typical of some larger geographical area (eastern Europe, northern Asia, southern Asia). Though I can't put my finger on it and say exactly what those patterns look like, nor pinpoint where the writer's mother tongue is, I can usually tell that something is off in a certain location-specific way. It's interesting and, to a certain extent, a fun exercise. It's a pity that I'm too lazy to sit down and compare samples of writing from different areas and come up with an organic and formal description of what I'm noticing, assuming that's even feasible without being a linguist and well-versed in all the languages involved.

No offense intended for the author of the parent comment, I hope he won't take this the wrong way either!