You’re seriously underestimating the governments ability to decipher a made up language. Bear in mind any government probably has entire departments dedicated to cracking codes and translation. Encryption is going to be a million times better than anything you can come up with. I’d just assume that if you can think it up, someone else can figure it out.
It certainly could be, especially if you’re not doing anything wrong. But if a government pries that much, you’d maybe be painting a target on your back by inventing a new language. You could also use an existing language that is hard to translate and learn, and isn’t well known. Like Ithkuil