First of all, welcome to Programming Puzzles & Code Golf! I'm thrilled you've joined our community.
There's no registration process for using a new language--just start using it! It's generally a good idea to include a link to information about the language and its encoding, as well as the location of a usable interpreter, in the post. That will be helpful for users unfamiliar with it and for challenge authors to test your submissions. It's fine if the interpreter has to be downloaded so long as it's available to download somewhere and there are instructions for how to get it set up.
Any answer can use any existing encoding so long as the answer works as expected when its source code is encoded using that particular encoding. For reference, here's our policy on answer encodingspolicy on answer encodings.
Let me know if you need any further clarification on anything, and again welcome!