Date picker is not localized

[hanzukun]

Steps to reproduce

1. Click date picker (which is localized correctly in long format)
2. See that the monthly calendar picker uses English short forms, ie Jan, Feb, Mar, Apr, May, ...

Expected behaviour

When picking a date in month popup it should show the date in user's locale.

Actual behaviour

The popup shows the month in English. This example shows Swedish in top (correctly localized), and English below (incorrect):

Calendar app

Calendar app version: 2.0.3

CalDAV-clients used: N/A

Client configuration

Browser: Firefox 74

Operating system: Ubuntu

Server configuration

Operating system: Ubuntu 18.04

Web server: Apache

Database: MariaDB

PHP version: 7.2

Nextcloud Version: 17.0.5

Updated from an older installed version or fresh install:
Update.

Logs

Web server error log (e.g. /var/log/apache)

No error.

Log file (data/nextcloud.log)

No error.

Browser log

Content Security Policy: Sidans inställningar blockerade laddningen av en resurs på inline (“script-src”). 2 utils.js:35:9
JQMIGRATE: Migrate is installed, version 1.4.1 jquery-migrate.min.js:2:551
oc_config is deprecated: use OC.config instead globals.js:26:15
Denna sida använder den icke-standardegenskapen “zoom”. Överväg att använda calc() i relevanta egenskapsvärden eller använd “transform” tillsammans med “transform-origin: 0 0”. injectStylesIntoStyleTag.js:201:10
Proxying an event bus of version 0.2.1 with 1.1.4 ProxyBus.js:72:14
Initial settings: 
Object { appVersion: "2.0.3", eventLimit: true, firstRun: false, showWeekends: true, showWeekNumbers: true, skipPopover: false, slotDuration: "00:30:00", talkEnabled: false, timezone: "automatic" }
settings.js:109:2
[DEBUG] calendar: The calendar app is using version 2.2019c of the timezone database 
Object { app: "calendar", uid: "authenticated:hans" }
ConsoleLogger.js:42:18
The escapeHTML library is deprecated! It will be removed in nextcloud 19. globals.js:26:15
[DEBUG] calendar: Current user principal is /remote.php/dav/principals/users/hans/ 
Object { app: "calendar", uid: "authenticated:hans" }
ConsoleLogger.js:42:18
The escapeHTML library is deprecated! It will be removed in nextcloud 19. 2 globals.js:26:15

[simonspa]

Moreover, the locale for formatting is not respected. I have German locale set with a week starting on Monday, but the picker looks like this for me:

starting with Sunday. (Also, observe the somehow missing padding - it's a bit weird because I'm using this since quite some time but just noticed now...)