As a speaker of Hijazi dialect, both means I miss you but اشتقت لك has a friendly meaning and I usually say it when I meet the person I've missed. ( I've missed you ) But I use the other one مشتاق لك when I still miss the person and still can't see or meet her/him. Anyway it conveys strong feelings so I use it when texting ( but rarely ) . ( I still miss you ) * The last one is مشتاق لك not مشتقلك

Thank you everybody!

I think what you wrote is used in Jordan ( as hamzah said ) and other countries but both of them are not commonly used in saudi instead, I will say : أنا رَاحْ أشتاق لك means I will miss you انا مشتاق لك means i miss you

I'll illustrate the difference with examples: أنا مشتقلك : I miss you أنا رَحْ أشتقلك : I will miss you. (رَحْ here means سَـوْفَ ) They are very commonly used in colloquial Jordanian, not so sure about Saudi Arabic though.