There is not a fixed rule or recommendation what you write when signing a book you want to give away as a present. Just be careful with terms you may find when searching for the German term "Widmung" (dedication) as this can be done by the author only.
Having said that, it is possible to write anything warm and joyful, probably you know better than us what meets your relationship to your friend.
If I was the recipient I'd probably love to see a quote of a Persian proverb you liked or that describes your relationship to your friend. You could even write in Farsi with a German translation added to make it more personal. It could also be a quote from the book.
یک معلم خوب باعث می شود مخاطبان را ببینید با گوش خو
Bei einem guten Redner fangen die Zuhörer an, mit den Ohren zu sehen.
You sure will quote the Farsi original much better than my Google translate attempt does.
After that you then just put a small greeting as space is limited, e.g.
Mit Grüßen aus dem Iran Ihr/Dein (signature)