There is no need to create new languages. But HPHC said that ancient languages follows some sort of rule that makes them powerful. So in theories, if you know these rule, you can create a language that has power. Again, it is unnecessary.
And is extremely time consuming, you would need knowledge in languages, like grammar (even if you want to create one without power).
If you want to make your writing more secure, than you can come up with symbols that represents a letter in a given alphabet, and simply use that language, but with your own letters.
It's a fun thing to do.