Arabizi is Arabic written in Latin letters, with digits standing in for the consonants Latin script has no letter for. Models handle the letters tolerably. The digits are what breaks, and they break at the tokenizer, before any model has seen the sentence.
The convention, and why it exists
Arabic has consonants with no Latin equivalent — pharyngeals and emphatics that English simply lacks. When Arabic speakers write on Latin keyboards, they substitute digits whose shape resembles the Arabic letter. The mapping is remarkably consistent across the region for the core set:
2 → ء (hamza, glottal stop)
3 → ع (ʿayn) — the digit 3 mirrors the letter's shape
