IMO to write down your thoughts just for your own usage, you can either encrypt your data if it is legal to do so, or you can write your thoughts on paper. Otherwise, check out this evergreen CrimethInc article about security culture.

I wouldn’t choose Elven Tongue or Klingon or similar fictional languages as a basis for a secret code because the people who code break are probably aware that those languages exist. Additionally, if I were a data scientist trying to sift through your communications trying to find coded text, the first thing I would classify is what languages are present. If Elven Tongue showed up, that is probably what I would look at first.

On that note, if I was trying to hide something, I would probably use a whole-word replacement scheme in a way that makes a whole sentence look normal. Even if the government collects all my data, do they really have the time to manually review all of it? Probably not; they’re probably going to use some kind of machine learning algorithm to search for “problematic” strings in their dataset and then flag whoever said them for further manual surveillance. If you think you are already an active surveillance target, then you might need to go with cyphers.

It’s probably a good idea to learn some code breaking. Lastly, Lemmy is a public social network. I wouldn’t put any plans that you ever intend to execute on this website or any of its instances in any form. It’s just not what it’s designed for. Best of luck.