Internationalizes a Next.js 16 App Router app with next-intl for fr/en/ar — every user string via t() and present in all three message files, locale routing, and Arabic RTL that mirrors via dir="rtl" plus logical Tailwind classes (ms-/me-, ps-/pe-, text-start) instead of physical left/right. Use when adding a translated string, wiring next-intl routing/middleware, fixing hardcoded text, making a layout mirror for Arabic, or converting ml-/mr-/text-left to logical properties. Not for Zod form schemas and field messages (see zod-forms) or the Tailwind theme and shadcn setup itself (see tailwind-shadcn).
