I will help Timelord a little by showing how you make the same mistakes in the English language
...
Why all the connected accounts make the same mistakes?
I'm not going to judge whether or not these users are alts, but the language mistakes are very small and very common. I think it's a safe guess to say millions of people make the exact same mistake, which makes it very thin evidence.
On top of that, certain language mistakes could be common to people who share the same (non-English) native language. Based on certain mistakes I can guess someone is Dutch for example.
I mean probably there was no need to look at his posting history, the transactions said a lot already.
But the language can be used to recognize similar writing styles. And after having a look at those posts I guessed they were from the same guy.
He confirmed anyway.