Murat,
Did you know the founder and Co-CEO of RIM (Mike Lazaridis) is actually Turkish?
I am in similar boat. I am studying Farsi and need a good Arabic script language pack for my Storm. Right now I am using Rosetta Stone but soon Ill need to practice on my Storm.
So far the Handango Store for Blackberry is the first resource I have found for language related programs. Below is a link for an English-Turkish-English dictionary for Blackberry. Hope this is a good starting point.
BlackBerry Software Store - powered by Handango
If I find more I will start a new thread.