Sti vs Questi
I recently discovered that "Sto, Sti, Sta, & Ste" are commonly used instead of "Questo/a/i/e." The word "stasera" also seems to derive from this shortening. I was wondering how common this is. Is it just informal or is it full blown slang?
It should be written 'sti, 'sto etc.
It's quite common in informal speech, not to be used in formal writing
This shortened form (technically, an apheresis) is a feature shared by several local dialects, in which 'sto and 'sta linger as a remnant of the Latin demonstratives iste (masculine) and ista.
Therefore, in everyday's speech the shortened form easily overrides the standard Italian questo / questa. It is now widespread even in areas where the original dialect would not drop the que- syllable.
It should not be used in the written language, and Duolingo should not accept it in exercises.
They're commonly used in INFORMAL spoken Italian. In formal situations, and in writing, they're to be avoided. BTW, it's spelled 'Sto or 'Sti, not Sto or Sti. There's an apostrophe, there, which stands for the missing letters, like "it's" as opposed to "it is." However, the word "stasera," is commonly used, even in formal situations. (Well, that was a convoluted explanation...hope you could understand.)