A few of my friends and I have been meeting up every so often for D&D, and we have a lot of fun. For the current campaign I'm DMing for them, I wanted to shake some things up: Maybe make some otherwise mundane and bland moments of the game a little more interesting. After a while of thinking, I had an idea: But I'm not sure if it's a good one.

My idea was to make writing for these languages: Actually creating an alphabet and unique writing style for languages in a campaign. For example, the party recently came into the possession of a holy book of prayers that they stole from representatives of a sun-worshiping organization. I hinted to the party that inside of this book may also be the locations of points of interest: If they can decipher the Celestial handwriting, that is.

Here's where my writing idea comes into play. If someone knows a language, I'll give them access to a 'cheat sheet' cipher that translates the text in question to English. They can't show the cipher to other party members, but they can help their fellow adventurers in translating the text. The text in question will be on a sheet of paper that I write up (using my own copy of the cipher), which I give to the party. Without the cipher, it would probably mean nothing, but the group can collaborate their efforts into deciphering the text.

Is this a good idea? I personally think this could be interesting to try out, but I'm also worried it may get boring. What are your thoughts?

I feel like if you guys are into a lot of roleplaying, it could be pretty fun. It would be decently interactive, and would be easy to use once you get the languages all written down. 

Many role play groups use strange symbols for some of their "foreign" languages - some use the Dwarf and Elf runes from Lord of the Rings.

If you are playing on a VTT like Foundry, then the VTT might support providing text in "gibberish" except it displays the real text for those PCs who have the required language on their character sheet.

For some tables, this could be really fun. 
To me though, it’s getting into a strange player knowledge vs. character knowledge area. If the character knows the language, they should just be able to read it in game. But you’re turning it into basically a decoding game for a player. It takes away a character ability (reading a language) and replaces it with a skill test for the player (not the character) making it about how good the player is at decoding rather then what the character can do.

Some people and some tables really love these kind of puzzle challenges. Others have people who’ll say “my artificer has a 20 int, can’t I just make a roll and know the answer.“ I guess what I’m getting at is, make sure you know your players and what they think is fun before you put the effort in. 
Also, will it be fun for you to sit there and watch them solve the puzzle? Because after you hand it off to them, there’s not really a lot for the DM to do. 

Quote from Xalthu >>

For some tables, this could be really fun. 
To me though, it’s getting into a strange player knowledge vs. character knowledge area. If the character knows the language, they should just be able to read it in game. But you’re turning it into basically a decoding game for a player. It takes away a character ability (reading a language) and replaces it with a skill test for the player (not the character) making it about how good the player is at decoding rather then what the character can do.

Some people and some tables really love these kind of puzzle challenges. Others have people who’ll say “my artificer has a 20 int, can’t I just make a roll and know the answer.“ I guess what I’m getting at is, make sure you know your players and what they think is fun before you put the effort in. 
Also, will it be fun for you to sit there and watch them solve the puzzle? Because after you hand it off to them, there’s not really a lot for the DM to do. 

I concur, especially about how fun it may or may not be. Were this to happen at my table where my character possesses the most Intelligence and Wisdom, I'd rather just roll for it or ask someone else to solve it. This has happened once already in a heavily modified Lost Mines of Phandelver game, where my character (a Grave Domain Cleric) should've been the most invested because it took place in the Neverdeath Graveyard... and I just went along maintaining the crypt while others solved the riddle. After about 30-40 minutes the riddle was solved, which I would've preferred to spend in conversation or combat.

It's things like this I don't play D&D for. It's like when there's a gambling den session or a carnival session, and people just sit around playing Poker or Hungry Hungry Hippos. If you like that, great, but ask the table if they're OK with that. Respect each other's time: if you're only playing four hours a fortnight or a month or whatever, do you really want to spend your session matching squiggles to letters? Now solving the puzzle out of session, that's another thing entirely: you could easily handwave the out-of-character solution in-game as "through your combined efforts you manage to solve the puzzle in a matter of minutes," and the amount of time saying that is all that's used, the game promptly resuming.

Now if this was like Swordquest where at the end I get a real-life sword (or would've done before Atari went down the pan), I'd be more inclined to participate.