The FullCalendar project welcomes PRs for new features, but because there are so many feature requests, and because every new feature requires refinement and maintenance, each PR will be prioritized against the project's other demands and might take a while to make it to an official release.
Furthermore, each new feature should be designed as robustly as possible and be useful beyond the immediate usecase it was initially designed for. Feel free to start a ticket discussing the feature's specs before coding.
Please link to a bug ticket in the description of your PR. If a ticket doesn't exist, please create one. The ticket must contain a reduced test case.
Please edit the source files in the packages/core/locales/ directory.