More notes for learners who might be interacting with 3arabizi on social media in vernacular Arabic:

Rare spellings

• 4 can also be ش, but on the whole, practically nobody uses 4 when "sh"/"ch" (ش) and "th"/"dh" (ذ) are there
• Maghrebis use 9 for ق. Most others don't use 9 at all, since ص is just spelled "s"
• 8 can also stand for غ, but again, virtually no one uses 8 over "q" (ق) and "gh" (غ)
• 6 is rare, and ط is usually just spelled "t"
• Only Egyptians use the apostrophes, and only a handful of Egyptians at that -- others spell those sounds based on their pronunciation

Variants

• The way you spell ق depends on its pronunciation, not its original Arabic-script spelling. That means it's "2" for people whose ق sounds like ء and "g" for people who pronounce it as a G. The Maghrebis who spell it with 9 pronounce it as an actual Fusha-style ق in their dialect
• Maghrebis mostly spell ش as "ch" thanks to French influence, whereas Egyptians pretty much only spell it as "sh" (with the rare "4" thrown in for kicks). Lebanese use and recognize both "sh" and "ch"
• Egyptians tend to go light on vowels (kinda like writing in the Arabic script) and spell ي as "y" at the ends of words. Others tend to go more by pronunciation and usually spell ـي with a vowel letter
• Even though I do think it's true that "others tend to go more by pronunciation", you can still find people doing whatever they like with vowels. Not everyone distinguishes "i" from "e" and "u"/"ou" from "o" in writing, even if they do in speech
• Some Lebanese avoid the letters 3, 2, or both by instead doubling up a nearby vowel. عربي can be "aarabe" instead of "3arabe", عدت can be "eedet" instead of "3edet", and وقت can be "waaet" instead of "wa2ret"
• The shaddah is almost never respected, even though it's pretty easy to represent it just doubling whatever letter. "Sawa" from someone Lebanese could either be سوا "together" or سوّى "he did", and you rely on context to figure it out -- some people will write "sawwa" for the latter, but not always. In fact, some people who know French will use "ss" just to represent any "s" sound