My group went with realistic rules about languages. First, there really isn't a 'common' language; humans have many languages, dialects, idioms, slang, and accents. English is a human language; so is Russian. Chances that a common English-speaking person would know more than say... 10 words in Russian? .01%?
We went with an expanded language list.
Some cities and areas are diverse. If your character is a rogue, and especially a smooth-talker, then s/he living in a port city with many different races would have a chance to know multiple words in multiple languages, and maybe even somewhat fluent in a few. So we went with percentages; 100% native in a language of choice (and maybe not race for orphans and displaced), and then 25% proficiency for common dialects in area of birth (because those dwarven merchants are copper-pinchers). If you visit a different country, chances are you/they will sound funny. Some words may not sound right (listening to the word 'aluminium' from an Englishman and an American will give you a hint, and the difference between a Ground Floor and a First Floor) and other words make no sense (I still haven't figured out what a 'lorrie' is, but I think it's a hill). for similar languages, we went 80% for off-country dialects and accents, unless the language was totally different (like English/Russian/Mandarin/Arabic where the alphabets have no commonality whatsoever), then it was 1% (because chances are, we know a word or two, like A-Kuta Matata, Swahili for 'No Worries' thanks Disney!).
To learn a language?
To anyone who has read a 'travelers translator' and then actually had to listen to someone talk in their native language knows what a pain that is. For someone who willingly learned another language later in life (like for myself, Kurdish Arabic and Pashto), translating is a real pain. You are not going to 'automatically' know another language. Anyone whose had to learn it not from childhood will still ask what some word means. For learned languages, we instilled a 25% proficiency rating. This made for interesting gameplay as our DM would hand us a letter that looked like an Ad Lib game (actually, he used those a few times) and we had to 'guess' what a letter meant ourselves (because our DM was evil like that).
Admittedly, never been much of a rule-follower, but if you feel that the rules don't cover what you want, there's nothing saying you can't instill a 'learning program' for your character to learn a language. If they're traveling with a dwarf, chances are your character might swear in dwarven, or know how to read the word 'ale' and such. The longer they're together, the more proficient s/he'll become. I doubt you'll be reciting Elvish Shakespere, but you might be able to tell an Elf that you'll kill him if you don't get your money right now!
For the sakes of Intelligence, we went with the score as a baseline of proficency, based upon the modifier. Percentage based upon the language + modifier = chance of translation. Time spent studying increased a players' starting percentage. Just because you have an 8 as an intelligence doesn't mean you can't know multiple languages; a person born in a multi-lingual area (like India) will inherantly know multiple languages despite their intelligence.
Food for thought.