A bilingual product is two first-class experiences sharing one codebase. Treating Arabic as an afterthought shows immediately.
Design for direction from day one
Use logical spacing (start/end, not left/right), mirror directional icons but not logos or media controls, and test long Arabic strings in every component.
Typography matters
Pick an Arabic typeface designed to pair with your Latin one, give it extra line height, and never letter-space Arabic — it breaks the joins between letters.
Engineering details
Keep copy in translation files, format dates and numbers with locale-aware APIs, and decide early whether to show Arabic-Indic or Western digits.