Jalali date Feature

Is your feature request related to a problem? Please describe.

I am writing as a Nextcloud user and on behalf of many Persian-speaking users to request the addition of official support for the Jalali (Shamsi) calendar in Nextcloud Calendar. For users in Iran, Afghanistan, and other Persian-speaking communities, the Jalali calendar is the primary calendar used in daily life, work, and planning. The absence of this option makes it difficult for us to fully adopt and rely on Nextcloud Calendar.

Adding support for the Jalali calendar would:

Significantly improve the user experience for millions of Persian-speaking users

Make Nextcloud a more inclusive and globally accessible platform

Reduce the need for external tools or unofficial workarounds

Given Nextcloud’s strong commitment to open-source values and serving diverse user communities, native Jalali calendar support would align very well with the project’s philosophy. We kindly ask that this feature be considered for prioritization, or that a rough roadmap or guidance be shared if possible.

If needed, the Persian-speaking user community would be happy to help with testing, feedback, or documentation.

Thank you for your continued work and dedication to the Nextcloud ecosystem.

Kind regards,
Mehrpaad Koulaeian

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Additional context

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The issue does not name files, tests, or an implementation entry point. Start by reviewing how Nextcloud Calendar currently handles calendar systems and date localization, then define the required Jalali behavior and affected user flows; done should mean documented native Jalali calendar support with appropriate tests.