Wrong first day of the week in Calendar with German localisation

Summary

The Calendar macro is displaying the first day of the week as Sunday when German localisation is set.

Environment

Confluence 5.9.6, 5.9.7
The bug is not reproducible in 5.8

Steps to Reproduce

1. Open Confluence Login page
2. Change the language to Deutsch
3. Login and Edit a page
4. Insert a Calendar macro or use the shortcut //

Expected Results

The first day of the week should be Monday

Actual Results

The first day of the week is shown as Sunday

Workaround

1. Browse to <confluence_install>/confluence/WEB-INF/atlassian-bundled-plugins directory
2. Backup the jar file confluence-language-pack-de_DE-6.0.0-OD-2015.50.0-0611-2015-12-04.jar
3. Open the original jar file, open the file i18n/aui_de_DE.properties
4. Modify the value of the attribute ajs.datepicker.localisations.first-day and set it to 1
5. Save the file and update the jar
6. Restart Confluence