Language Fluency

I am likely not the only one, but I have always been a little dissatisfied with the binary nature of D&D languages. I rather like the idea that if a character knows more than one language, that they have different levels of comprehension in each. If i meet a polyglot, they are likely not idiomatic in more than one or two languages, and have varying levels of fluency. I think the same should be true for adventurers. Languages are often glossed over in roleplaying, and in almost every group it tends to become a game of the party covering the most bases by allocating their known languages, even if this makes little sense thematically.

Most of the Runequest/BRP games have something like this, where you have a percentile skill for languages and cultures, and I think that is pretty neat. Here's my take on it:

Fluency at Character Creation

At creation a character gets Mannish (the common tongue) and their native language to start with. Fluency in their native tongue is always 100%. If they are not human or are not from Mannish lands, they must roll a d50 plus 50 plus their Intelligence score (maximum 100, of course) to determine their fluency in the common tongue. Fluency of over 50% means that they are also literate in the language. 

For every point of Intelligence modifier a character has, they are also able to speak another language. For these additional languages, roll 1d100 plus the character's Intelligence score to determine fluency. 

If it is a dead language, the character is automatically literate, and a score of 50% or higher means they can also speak it properly.

Most of the time, a character would not need to determine whether or not they understand a language. Any fluency at all, even 1%, means a basic survival understanding of a tongue. However, in ancient ruins or tombs, where there is little context for translation, knowing the precise text on a tall or stone tablet is a life-or-death proposition. Roll under your fluency score on a d100 to see if you understand it completely. The DM is encouraged adjudicate just how well or poorly the piece is translated based on the roll, and may want to make the roll in private if that is their playstyle.

Perhaps characters can increase their fluency if exposed to a language; 20% per year if passively living in a region, 5% per month of dedicated study. Secret languages, dead tongues, and non-verbal modes of communication may not be learned passively.