Updated PLANS.md, AGENTS.md, and arabic-localization.md to reflect the “foundations now, full translations later” approach and marked progress accordingly.

Implemented localization foundations across backend and frontend (locale settings/middleware, preferred language, i18n wiring, RTL support, minimal Arabic UI strings, Accept-Language).
Added targeted backend and frontend tests plus a risks note for pending full translation coverage.

backend/apps/payments/serializers.py

@@ -1,4 +1,5 @@
 from rest_framework import serializers
+from django.utils.translation import gettext_lazy as _
 
 from apps.bookings.models import Booking
 from apps.payments.models import Payment, PaymentProvider, PaymentStatus
@@ -33,7 +34,7 @@ class PaymentCreateSerializer(serializers.ModelSerializer):
 
     def validate_booking_id(self, value):
         if not Booking.objects.filter(id=value).exists():
-            raise serializers.ValidationError("Booking not found")
+            raise serializers.ValidationError(_("Booking not found"))
         return value
 
     def create(self, validated_data):