calendar date picker (in public link) should honor locale settings

Steps to reproduce

1. install calendar 3.1.0
2. set preferred language in sharee's browser to non "en-US", e.g. "[de]" in Firefox
3. set locale of the sharer to non "en-US", e.g. "German (Germany)" in NC's personal settings
4. create appointment (public link)
5. open that link in a (private) browser window and check date selection widget

Expected behavior

In private/public shared links, the calendar date picker widget should honor locale settings – ideally those of the remote user trying to make an appointment, or at least the locale settings of the NC user that shared the appointment.

Actual behaviour

unlocalized calendar (US locale, Sunday first) is used for the date picker

Calendar app version

3.1.0

CalDAV-clients used

Webinterface only

Browser

Firefox 97.0.1

Client operating system

Arch Linux

Server operating system

Arch Linux

Web server

Nginx

Database engine version

MariaDB

PHP engine version

PHP 8.0

Nextcloud version

23.0.2

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

Enabled:
  - accessibility: 1.9.0
  - activity: 2.15.0
  - admin_audit: 1.13.0
  - appointments: 1.12.0
  - apporder: 0.14.0
  - backup: 1.0.4
  - bookmarks: 10.0.3
  - calendar: 3.1.0
  - circles: 23.0.1
  - cloud_federation_api: 1.6.0
  - contacts: 4.0.8
  - dav: 1.21.0
  - deck: 1.6.0
  - federatedfilesharing: 1.13.0
  - federation: 1.13.0
  - files: 1.18.0
  - files_external: 1.15.0
  - files_frommail: 0.4.0
  - files_mindmap: 0.0.26
  - files_pdfviewer: 2.4.0
  - files_rightclick: 1.2.0
  - files_sharing: 1.15.0
  - files_trashbin: 1.13.0
  - files_versions: 1.16.0
  - files_videoplayer: 1.12.0
  - groupfolders: 11.1.2
  - impersonate: 1.10.0
  - logreader: 2.8.0
  - lookup_server_connector: 1.11.0
  - mail: 1.11.7
  - notes: 4.3.1
  - notifications: 2.11.1
  - notify_push: 0.3.0
  - oauth2: 1.11.0
  - password_policy: 1.13.0
  - polls: 3.5.4
  - privacy: 1.7.0
  - provisioning_api: 1.13.0
  - ransomware_protection: 1.12.0
  - richdocuments: 5.0.2
  - serverinfo: 1.13.0
  - settings: 1.5.0
  - sharebymail: 1.13.0
  - spreed: 13.0.3
  - systemtags: 1.13.0
  - tasks: 0.14.2
  - text: 3.4.0
  - theming: 1.14.0
  - twofactor_admin: 3.2.0
  - twofactor_backupcodes: 1.12.0
  - twofactor_email: 2.1.1
  - twofactor_gateway: 0.19.0
  - twofactor_nextcloud_notification: 3.3.1
  - twofactor_totp: 6.2.0
  - twofactor_u2f: 6.3.0
  - updatenotification: 1.13.0
  - viewer: 1.7.0
  - workflowengine: 2.5.0
Disabled:
  - auto_groups: 1.4.0
  - bruteforcesettings: 2.3.0
  - comments: 1.11.0
  - contactsinteraction: 1.1.0
  - dashboard: 4.0.5
  - encryption: 2.0.0
  - firstrunwizard: 2.2.1
  - group_everyone: 0.1.9
  - nextcloud_announcements: 1.5.0
  - photos: 1.1.0
  - recommendations: 0.4.0
  - support: 1.0.0
  - survey_client: 0.1.5
  - user_ldap
  - user_status: 1.0.0
  - weather_status: 1.0.0

Nextcloud configuration

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "cloud.datenschutz-individuell.de",
            "stage.datenschutz-individuell.de",
            "cloud.selbstbestimmt-digital.de",
            "stage.selbstbestimmt-digital.de",
            "cloud.seyfarth.de",
            "test.seyfarth.de",
            "cloud.owncube.com",
            "efdpo.owncube.com",
            "cloud.bvdnet.de"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "23.0.2.1",
        "overwrite.cli.url": "https:\/\/cloud.datenschutz-individuell.de",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "maintenance": false,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "dbindex": 1,
            "timeout": 1.5
        },
        "logtimezone": "Europe\/Berlin",
        "trashbin_retention_obligation": "auto,30",
        "versions_retention_obligation": "auto,366",
        "skeletondirectory": "",
        "default_language": "de_DE",
        "default_locale": "de_DE",
        "default_phone_region": "DE",
        "updater.release.channel": "stable",
        "theme": "",
        "loglevel": 2,
        "data-fingerprint": "adca8c722278d40310becb30b3e20c5e",
        "mail_smtpmode": "smtp",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_sendmailmode": "smtp",
        "mail_smtpport": "25",
        "mail_smtpsecure": "tls",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "simpleSignUpLink.shown": false,
        "twofactor_enforced": "true",
        "twofactor_enforced_groups": [
            "admin",
            "_Mitarbeiter"
        ],
        "twofactor_enforced_excluded_groups": [
            "_Upload"
        ],
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "app_install_overwrite": [
            "files_frommail",
            "files_mindmap",
            "apporder"
        ],
        "htaccess.IgnoreFrontController": true
    }
}

Web server error log

no relevant entries

Log file

no relevant entries

Browser log

no relevant entries

Additional info

No response

No source files or tests are identified in the issue. Reproduce the public-link date picker with German browser and Nextcloud locale settings, then trace the calendar frontend's locale initialization. Done means the picker no longer defaults to US formatting and honors the remote user's locale or the sharer's locale.