RPGMemes

Depending on what skill they are rolling, a nat 20 doesn't necessarily mean they just instantly have all knowledge of the thing they are deciphering.

Let's say it's an ancient form of Elvish, and the character speaks Elvish. They'd know modern Elvish, and might be able to use that to discern enough to get the general gist of the writing, but not a perfect translation. Which could come into play later on to hilarious effect.

If they used uh... I forgot the skill name but the generic "adventurer knowledge" one, they might not know what it says at all, but they may be able to know what language it is, who wrote it, and what they might expect based on knowing about the script in other dungeons.

If it's an arcana check they could understand it is magical, and what it does; maybe activate/deactivate it but not how to recreate it or translate it, per se.

I actually now want to make a character that's just super knowledgeable. No ability to fight, or even cast magic. They just know everything about everything.