Arcydea allows Downtime, which allows characters to extend or improve their skills and attributes, take on new feats, learn or develop new spells, and more. When working on a specific task, Downtime hours are tracked simply (began working on X on 4/30), and accumulated as the sheet is updated.
In addition, Downtime days may be awarded for adventures that take more real time than character time (two weeks to finish a plot that resolves in two days means 12 days of downtime) or more character time than real time (a plot that resolves in a week from a character's perspective that is played out in one evening adds 6 days of downtime.) These are effectively additional adventure rewards, and XP rewards may be adjusted accordingly.
Arcydea allows characters to expand and grow in ways not quite covered by DND 5e RAW, and modifies the systems provided in the PHB and DMG significantly. As such, the relevant options are provided below.
Learning a Language. You automatically know the languages available via RAW; however, you can gradually learn additional languages with Downtime. Note that if you are in a country that constantly speaks a language you are trying to learn, all Downtime spent is doubled (as you are basically spending every waking moment practicing). Downtime is cumulative; on the first day you learn a few basic phrases, by day 5 you can manage simple conversation with difficulty, by day 10 you can manage a broken but generally complete conversation, and so on. Effective Downtime is halved if you do not have a teacher or speaker to practice with and are self-taught.
A few phrases: Just enough to get by. 2 hours to learn three spoken or written phrases.
Smattering: This isn't enough to actually carry on a conversation, but will help you understand some basic words. 10 hours to speak or write, 20 hours for both. You can make a Intelligence check to get very general concepts spoken by someone in this language, or to parrot specific common sentences (like “where is the bathroom”).
Broken: A broken form of a language takes 20 hours to learn to speak or write, or 40 hours to do both successfully. Broken language allows you to carry on a generally complete conversation without Intelligence checks, although difficult concepts may still be beyond your reach.
Accented: An accented form of a language takes 40 hours to learn to speak or write, or 80 hours to do both successfully. This allows you to carry on a conversation, although you will have difficulty disguising your accent or understanding specific dialects.
Accented characters with Mimicry in some way or another (the Mastermind's 3rd level class feature, for instance) can convincingly pass as Fluent speakers if they have someone to mimic; however, they still will not understand regional differences in actual language used. (In English terms, one could convincingly mime a regional American accent despite not being fluent, but the difference between soda, cola, and pop would still throw them for a loop.)
Fluent: Fluent understanding of a language takes 100 hours to speak or write, or 200 hours to do both successfully. This allows you to understand even odd dialects of a language, to be able to convincingly manage accents (when combined with Performance), and generally to know the language you're speaking or writing.
Attribute Development: By training in your downtime, you can increase an Attribute (to a limit of 20) by +1, with 200 hours of training with someone who has a higher Attribute; halve Downtime gains if you are training by yourself or with someone who doesn't have a higher Attribute.