I think we're past trying to assume peoples identities based on writing styles, it's too easy to fake for the hackers, simply drop 1% of the words you're using and now suddenly people think you're no longer a native English speaker.
And not only is it easy to guess wrong or easy for the hacker to fake, it also adds absolutely nothing to the story/evidence/history by trying to guess the country they are from. If you're right, nothing has been gained. If you're wrong, you've just blamed the wrong nationality, again with no gain if you're right.
This is a bit of my point. If I'm from Uruguay (and not native English speaker) and I want to to be a anonymous user that wants to pretend to actually be Slavic, I can easily look up common mistakes (like missing `is`) in order to foster the image of me being from somewhere I'm not.
Typing in a way you don't usually type is a common way to mask more of your identity.
https://sites.google.com/view/hackersconfession/home/hacker-...
How about Vietnamese?