There's no "proper" English, but there are many "improper" ones. If your P becomes so misshappen that it can be seen as a D, you aren't communicating anymore.
It's the same thing for words: u, m8, w8, pwn aren't proper per se but have a clear and unambiguous mapping to the proper word. Even when using misspellings like seperate or convinsable, you are still communicating clearly enough.
It's only when you use the spelling of a different word that you screw up. Errors such as board/bored, hoard/horde, straight/strait send a sentence straight into damnyouautocorrect, if not Alice's Wonderland. You cannot "evolve" a word by having treasure and army become a single concept, unless you want to speak Smurf. And even then, they can smurf which smurf means smurf.