Can you use "hedefim" instead of "amacım?"
Of course :)
Why does "amaç" becomes "amacım" when conjugated?
Read this: https://www.duolingo.com/comment/9040173
Many words that end in a t, k, p, or ç undergo consonant mutation :)
What is the difference between 'hadef' and 'amaç'?
*Edit: I have already found an answer! (Amaç: aim, purpose, objective; Hadef: goal, tarject, objective) (orde90 commented that)
kullanmak is not accepted. Is it wrong?
Yes it is wrong. "Kullanmak" = "use"
We've used beklemek for speaking languages so far in every other sentence. Why doesn't it work here?
Is it possible you confused 'beklemek' with 'bilmek'?
I suppose "Benim amacım Türkçe bilmek" also would work?
"My aim is to speak Turkish."
Translation: Benim amacım Türkçe konuşmak.
Amacım Türkçe konuşmak.
Correct other Turkish answer accepted by Duo.