Which do English talkers recognize "I want to fix it." as (1) "I want to modify/change/repair it" or (2) "I don't want to modify/change/repair it anymore"? Since the both have the opposite meaning in the software engineering, I often confused it. I also want to know whether the English talkers has the same confusion in this word.
It depends on what "it" is,
For example, if "it" is "the date of the next meeting", then "fix it" must mean "don't change it anymore", since the repair meaning doesn't make sense.
On the other hand, if "it" is "a bicycle", then "fix it" must mean "repair it", because nobody wants their bicycle affixed to something.
There is rarely any confusion, unless done deliberately as a joke. When speaking of things that should not move, then "fix" means "prevent from moving". When speaking of things that should move then fix means "repair".
I'm a native English speaker. I cannot bring to mind any example of "fix" having your second meaning. I understand it to mean:
I want to modify/change/repair it
I work as a Software Developer and if I'm fixing something I want to do a complete job; I don't want to create new problems as I fix the existing ones. Hence
I don't want to keep fixing it
so in that sense
I don't want to repair it anymore
is true, but that's because I've fixed it properly!