Why Facebook About section’s description shows characters limit error when I did not exceed the limit?

I am trying to add a description to a Facebook page’s About section. But it displays an error

Description (436 characters) exceeds the 255 character limit because of the special characters added. Please correct and try again.

while I only wrote less than 255 characters. I am writing the description in Arabic. I do not know what it means with special characters. There is only commas and dots plus the Arabic letters. Here is the part that was accepted, شركة الهيثم, شركة متخصصة فى انتاج البرمجيات, تستخدم قواعد بيانات شركة اوراكل العالمية فى بناء جميع انظمتها. توفر وسيلة سهلة, مرنة ودقيقة
And that’s the completion of it that was not accepted, للتسجيل البيانات الهامة والاطلاع على التقارير والاحصائيات التى توضح الوضع المالى للنشاط قيد الممارسة.