This is an official ZX Spectrum licensed by Amstrad.
The machine was developed by Matisco Trading & Inv. Co. (شركة ماتيسكو للتجارة والاستثمار) of Cairo, also known as Sinclair Egypt (سنكلير مصر).
The ROM was developed by Dr. Nabil Nazmi of the University of Cairo.
The Arabic boot screen reads:
اختيارات
لغة إنجليزية
لغة عربية
سنكلير مصر
meaning:
Choices
English language
Arabic language
Sinclair Egypt
The Arabic copyright reads:
© ١٩٨۷، ١٩٨٨ سنكلير مصر
تقديم: شركة ماتسكو
وكلاء سنكلير وأمستراد مصر
اعداد: د. نبيل نظمي
الوحدتان أ: و ذ: متاحة .
meaning:
© 1987, 1988 Sinclair Egypt
Presented by: Matsco Corporation
Dealer of Sinclair and Amstrad in Egypt
Prepared by: Dr. Nabil Nazmi
Drives A: and M: are available .

Unlike the other Arabic ZX Spectrums (+, 128, +2, +2A) which only supports 48K mode when switched to the Arabic language, the +3 has a fully translated 128 ROM and a seperate 48K mode. Interestingly where the English 48K mode of the +3 says “© 1982 Amstrad”, the Arabic 48K mode of the +3 says “© 1987 Sinclair Egypt” instead.
There is a small daugtherboard installed which handles the language selection.
The language can also be selected from witin BASIC: if the computer is in English mode, typing OUT 65503,255 will switch it to Arabic without rebooting. OUT 65503,254 (keys OVNZ 30556,452 to spell out خروج) will switch back to English.
Thank you Mohammed Habib for your 10 years of research on this subject.