When you say Turkish characters are replaced do you mean like this
reference chart and if so which characters.
These forums don't display other languages very well so rather than post them here just tell me which characters in the alphabet here at the top that are not working as expected:
http://en.wikipedia.org/wiki/Turkish_alphabet
For example "Lower case 4" would be the "Lowercase C-cedilla" or give me the name from the "description" column of the chart from above "reference chart".
When export content compiles data to be moved from Joomla 1.0+ to Joomla 1.5+ sites it attempts to convert any characters in the high range (those in the chart) to their numeric equivalent so it will be a smooth transition to UTF-8.
A few questions:
What version of PHP is on the source and destination sites?
Is iconv enabled on the server or servers?
At what stage do you noticed the characters are not being decoded?
What do you see after you import the data and look at an article via the edit feature in export content?
Are you using the standard Joomla editor?
Have you got a link to either site?