What is the diffrent berween " i " and " ı " in Turkish?
They are two different vowels, like ö and o or ü and u.
i ö ü (the "dotted" vowels) are front vowels; ı o u (the "undotted" vowels) are back vowels. e is also front and a is also back.
Replacing i with ı or the other way around would be like mixing up any two vowels, like writing "bad" instead of "bed" in English, for example -- the two are separate vowels.