Is ; a good string parser delimiter ?

I think it depends on what your string will be. If you create the string yourself, you may use this delimiter and avoid the ";". If someone else creates the string, I think you'd rather use "|".

If there aren't any semicolons in the strings you want to delimit, yes.

Surmulot is right. If this delimiter is used in strings with player-input, then ";" might be used... But "|" could be used too (in smileys for example :|).
I currently use "|" much, but i make tests to avoid this kind of problem, and I try to use player-input at the end of the tokenized string, so that it won't matter much :
/PrivateMessage|Corentin|Rushino| hey :| Here's my private message to you Rushino
will not result in a big problem.
/PrivateMessage|hey :| Here's my private message to you Rushino|Corentin|Rushino
Would be more complicated....

Remember that client-side tests aren't enough, a hacker could send text containing your delimiter without using your client, but with another app

They could also send it using your client with a tool like WPE, no matter how much protection you put in client side.

Interesting... how about * ? that will never be used...

I am using the #.

I use stuff like ±.

I use "¤" because this character is never used.

and using a combination of odd characters (i.e. "|+") would increase the odds that someone would use them.