Date picker not working when Jira is using Danish

Summary

When editing a Date Picker field (Due Date, for example), when Jira default language is set to Danish/Portuguese/Slovencina/Swedish, the date filled when the user clicks on the calendar icon and picks a day is filled with an invalid format.

Examples

In the Danish example, after selecting the date from the calender, it is forcing the month to be followed with an additional period '.'

14/nov/18
Vælg en dato
Ugyldigt datoformat. Indtast en dato i formatet "d/MMM/yy".

However, entering a value such as '14/nov./18' will work correctly but users need to manually correct the
date by entering the period '.'

Steps to Reproduce

1. In the system administration panel, switch the General Setting of system language to a language such as Danish, Portuguese, or Slovenia
2. Access a ticket on Jira
3. Click on Edit and modify a Date Picker field value, by choosing a date after clicking on the calendar icon next to the field.
4. Attempt to save the date changes

Expected Results

The date is filled correctly according to the language pack.

Actual Results

Jira returns an error message that the date format is invalid. However the javascript date picker, java input format, and look and feel settings are correctly set.

Workaround

This is not reproducible when using the d/MM/yy format (9/6/16 for example), so users can do the following to change the format:

1. Go to Administration > System > Advanced Settings
2. Change the following parameters:

   jira.date.picker.java.format = d/MM/yy

   jira.date.picker.javascript.format = %e/%m/%y

   jira.date.time.picker.java.format = dd/MM/yy h:mm a

   jira.date.time.picker.javascript.format = %e/%m/%y %l:%M %p