Set dir="rtl" and the layout flips. Ship it, and Arabic users will tell you within a day that something feels off — usually without being able to name it.
Typography is not symmetric
Arabic letterforms carry more vertical complexity than Latin ones. A line height that looks generous in English is cramped in Arabic, and letter-spacing — a common Latin refinement — actively breaks Arabic script by pulling connected letters apart.
Not everything mirrors
Layout mirrors. Progress bars mirror. But a play button still points the direction media advances, phone numbers keep their order, and code samples stay left-to-right. Blind mirroring produces interfaces that are technically RTL and practically wrong.
Numerals are a choice
Saudi corporate and government interfaces overwhelmingly use Western digits in Arabic text. Switching to Eastern Arabic numerals because it feels more authentic usually reduces comprehension for the actual audience.
Forms need more room
Arabic runs shorter than English in some places and considerably longer in others. Labels that fit a fixed-width column in English will wrap in Arabic. Design the Arabic form first and the English one will fit comfortably; do it the other way and you will be patching for weeks.
Test with real content
Lorem ipsum hides every one of these problems. Use real sentences, real names and the longest label you actually ship.