thanks for your warning. I actually still am a student at the university, currently enrolled in my last semester which officially just started. I don't have all my grades yet and i haven't yet graduated. Through some coincidences though, i am in the situation that I don't have anything to do anymore for my degree after August 31. The semester ends on December 17. I have already a flight booked to leave the country on September 19. So I am certain that I won't have any trouble concerning my status as a student. I'm just wondering about cancelling my extension before actually graduating on paper.
the letter states that my last day of studying is sometime end of December but I actually already finished all courses and exams so i would like to cancel before. Would that pose any problems?
you can buy a thai-book for primary school students at most book shops, they're inexpensive and if you know how to read Thai you'll find it all explained there (though it's explained in examples and not in "rules"). If you want to know the linguistic rules, a thai dictionary won't do, you'll have to get scientific works of the thai language which you probably will have to get through a university.
it is. Your example of "l" and "r" is not case of "breaking the rules" in daily life but it is due to the phonological similarity of ล (l) and ร (r) in the thai language.