[suprjami]

This reminds me that as a child I taught myself Tolkien's runes from The Hobbit, which is mostly another substitution of the modern English alphabet:

https://en.wikipedia.org/wiki/Cirth#Runes_from_The_Hobbit

I got to the point I could read and write without a reference. Not as fast as English but not slow either.

Many years later I found a notebook with many pages of things I'd written but had since lost the ability to read again.

[Terr_]

I remember writing to friends using a Pigpen Cipher [0], which I probably first encountered in some sort of Super-Mario themed workbook or magazine page.

[0] https://en.wikipedia.org/wiki/Pigpen_cipher

[nozzlegear]

I have a very similar story, except I taught myself and a friend to write using "daedric" from Morrowind. I don't know if it was the actual daedric letters from the game, I think I just found a font that claimed to be daedric from a website and thought it was really cool. My friend and I would write notes to each other in this little secret chicken scratch-looking alphabet, it was fun.

I sometimes try to remember how to write it or how to read it (I still have some notebooks from when I was a kid as well), but it's been 20+ years and I only recognize a few characters at this point. The rest is practically Greek to me now.

[dEnigma]

I learned the Daedric letters from the physical map that came with the game, which had the place names in both Daedric script and English.

[ronjakoi]

I don't speak Korean, but I'm a language nerd. Sometimes for fun I write Finnish in the Hangul alphabet in my journal (requires some approximation/adaptation).

[Carrok]

I learned very similar runes for the Ultima games.

[khedoros1]

Those are the ones that I learned, from the magic system in Ultima Underworld. I think that H and W are swapped, and that Tolkien's alphabet includes a few more letters. They're both similar to the Elder Futhark runes, if I'm remembering correctly.