Infer nationality, native language, whatever, of writer based on how they use English

It's not immediately clear how you'd train this. Location subreddits, for example - /r/northernireland has a subscriber count implying most users there don't actually live in Northern Ireland...

The title is descriptive enough, but if it's not, I'm talking about how "Euro English" gives someone away as European, "if ... would be ..." instead of "if ... were ..." narrows them down to German or Dutch, "graduate" in the same paragraph as "18" probably makes them American or Americanised-ESL as no non-American native English speakers "graduate" from anything other than university, etc. And, of course, American and non-American spellings of a word may differ.

Basically, there are textual equivalents of a person having an accent. Sometimes you actually have to read quite alot of text to make an inference by eye. Automate this.