I like how Lamentations of the Flame Princess handles languages and thought I would make my own rules. Here’s a rough write up:
Characters begin play being fully fluent in their native tongue. They are also assumed to be literate. Clurichauns, Elves, Half-Orcs, and Dwarfs will know the ‘Common Tongue’ used by most of the kingdoms of men in addition to their racial tongue. Devilkin, Halflings, and Orgar do not have their own language, instead speaking the Common Tongue.
When a character comes into contact with another language have them make a D20 roll verse a DC 10. Add the character’s Int modifiers but NOT his levels. If the character rolls at or above the DC he knows the language having learned it sometime in his past. If the roll fails he does not know the language. He cannot roll again for that particular language.
By default, the DC for this roll is DC10. However, if the language is somewhat obscure the DC is 14. If the language is considered exotic the DC is 18. If it is an ancient, dead language the DC is 22. Modern day equivalents for an English speaker might be:
Spanish, French, German – DC10
Russian, Turkish – DC14
Farsi, Japanese – DC18
Aramaic, Sumerian – DC22