There is a discussion on Google Plus about determining languages randomly and how this might change the dynamics of the reaction roll to potentially include PCs other than just the one with the highest charisma. Here is a simple system based around that idea, which also incorporates other, general skills. This approach was influenced by the method of language determination in LotFP, the DCC skill system, and Numenera (which I am currently reading). This is not part of any larger rule set, and was written to easily integrate with any old school fantasy game.
PCs begin with 1 skill slot, plus one additional slot for each language or intelligence bonus (depending on the base system). An additional skill slot is added every time a level is gained. The number of slots is kept intentionally low to begin with for ease of use, but referees may begin characters with a larger pool of skill slots if desired. A character’s native language does not require the use of a skill slot.
Determining Skills & Languages. When confronted with a situation where speaking a language or having a skill would be advantageous, a player may make an intelligence check. If successful, the player’s character speaks the language or has the skill. Otherwise, the skill or language should be noted in a list of missing skills or languages (the character may gain training in these absent skills at a future time, but may not gain access to them using an intelligence check in the moment as described here). If the intelligence check is a critical failure, the PC in question simply does not have aptitude for the language or skill and may not attempt training of that language or skill in the future. Note this on the list of absent skills. This is essentially a way of retroactively determining part of a character’s past without needing to plan it beforehand. Further explanatory backstory can be developed if desired, which can be good fodder for detailing aspects of a setting that had hitherto been ignored.
Skill Scope. The scope of a skill should be slightly beyond the immediate task at hand and should be something that a person within the game world would recognize as a field of study or training. “Carpentry,” for example, rather than “building things.” Characters may take the same skill more than once if desired (pending successful intelligence check), and each time the skill is taken is recorded as a degree of specialization. Some referees may prefer to limit skills to one degree of specialization in order to encourage skill diversity. Consider requiring literacy as a separate skill for settings where learning is rare and precious.
Using Skills & Languages. Having access to a skill or language gives a character a basic level of competency which does not require any die rolls. For example, a character that speaks a given language can communicate in that language without any chance of failure and a character trained in carpentry can build a chair given wood and tools. Skills also allow you to make related ability checks using two dice, taking the best result (each degree of specialization adds another die).
Development Through Play. It is suggested that the skill and language lists be allowed to grow organically along with the campaign events. The PCs will naturally end up speaking languages and having the skills relevant to the challenges faced, so there will be no confusion at character creation about what languages will be useful. This is especially useful if the referee does not know or has not decided such setting details at that point. That said, players with a strong character concept may preselect particular skills at the time of character creation (referees may still prefer to require an intelligence check). Mechanically, by preselecting skills, players gain predictability of character competence (which can be used for creative planning) in exchange for giving up flexibility during play.
Random Languages. One benefit, from a game standpoint, of determining languages randomly in this way is that the character with the highest charisma in the party may not be the character that speaks a particular language. This makes the reaction modifier of all PCs potentially relevant. Be sure to use the charisma modifier of the interlocutor when making any reaction rolls. As a referee, consider rolling to determine if a group or creature encountered speaks a new language, if you have not already determined that part of the setting. Consider making languages based on location rather than race (as is commonly done in fantasy games), as this will make every town encountered potentially foreign. This can be used as a method to help develop a setting through play much like characters are described as developing through play above.
Training Skills. Players may spend their downtime action between sessions to gain training in a skill. This may require paying for training or locating a teacher, especially for more obscure or esoteric skills, as ruled by the referee. The process is otherwise the same as checking for a skill during play: make an intelligence check, and so forth. Failures may be retried, but this requires another downtime action between sessions (and may require further expense or teacher reaction rolls; teachers may become frustrated with students that are slow learners). If the intelligence check is a critical failure, the PC in question simply does not have aptitude for the language or skill and may not attempt training of that language or skill in the future. Note this on the list of absent skills.