"Add Arabic support" sounds small — until the site opens. The causes repeat across almost every project, and all of them are avoidable if you know them up front.
1. Physical instead of logical properties
margin-left, padding-right and left are direction-locked. The logical equivalents — margin-inline-start, inset-inline-start — flip automatically with the document direction. Using the physical ones means maintaining two layouts.
2. dir="rtl" on its own
It flips overall direction but not directional icons: the arrow meaning "next" must point left in Arabic. Arrows, carousels and progress bars all need explicit mirroring.
3. The wrong font
Latin fonts carry no Arabic glyphs, so the browser substitutes a fallback — which is where "Arabic looks bad on our site" comes from. Arabic also needs more line-height, because vowel marks stack above and below the line, and letter-spacing reset to zero, because tightening breaks the joins. When the damage is already done — text out of Photoshop or a PDF, reversed or with its letters detached — our repair tool puts the characters back in order.
4. Search that does not understand Arabic
الكتاب, كتاب and كتب share a root; naive search sees three unrelated words. Add that users type without vowel marks while the stored text has them — or type in Latin letters entirely, which is why we built a transliteration engine.
5. Input validation
Fields that reject Arabic names, phone inputs expecting one format, dates with no Hijri option. The damage concentrates on the signup form — the first thing a customer meets.
The practical rule
Build Arabic-first. Translating afterwards surfaces every one of these late, and fixing them post-launch costs more than avoiding them — it is one of the largest lines in what an e-commerce site really costs.