Can i create my own and use it legally even if it insults others?:
If you do it in GOOD FAITH it is fine.
However if you are doing in in order to yell "I have a bomb!" in public places and then justify it by saying you were speaking in your new language -- and it was your ONLY real purpose in coming up with a new language in the FIRST PLACE -- Then it will not help you, and you WILL be convicted of "making terroristic threats".