Date picker not working when Jira is using Portuguese, Solvenia, Danish, Swedish, Dutch, Russian, German

Summary

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

Examples

For example, in Portuguese-PTBR it is expected a date like 6/set/16 and the date picker fills as 6/Sep/16, throwing an error for the date format.

In the Danish example, all months selected (Except Maj or May) all appear to be forcing their abbreviations 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 (except for the month of may which is not technically abbreviated with only 3 characters).

The same happens with Russian language, forcing months' abbreviations with an additional period '.' 

Environment

• Jira 7.2 or 7.2.1 with a translation pack (tested with Portuguese-PTBR and Slovenian)
• Jira 7.12.3 with Danish default language set
• Jira 8.19.1 with Russian default locale language set

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.

Notes

This bug ticket was originally indicating that the translation pack might have been the cause of this problem. However upon further investigation it appears that Jira itself is not correctly handling regional differences in regards to month names and their appropriate abbreviation to that region / locale. For Danish this is particularly difficult because the region appears to require that 3 letter month abbreviations end with a period. The Javascript date picker can be configured to adjust to that, but not for the month of May/Maj.

Workaround 1

https://confluence.atlassian.com/jirakb/cannot-start-sprint-when-user-profile-language-set-to-german-running-adoptopenjdk-11-0-11+9-1063174418.html

Workaround 2

For Portuguese, Dutch:
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