Date picker shows 'undefined' on Project Release pop-up if the language is set to Russian, French, German or some other language

Summary

Date picker shows 'undefined' on Project Release screen if the language is set to Russian, French, German or some other language

Steps to Reproduce

1. Set JIRA language to Russian
2. Go to Project > Releases
3. Click three dots (Actions) by the version you want to release > select Release
4. Open the date picker in order to change the date

Expected Results

Calendar shows dates as expected.

Actual Results

Calendar shows 'undefined' instead of dates:

Workaround

Workaround 1

Set language to English in your User profile before releasing the version.

Workaround 2

Set the version's release date before clicking the Release button. This can be done Project settings > Releases > press three dots (Actions) button > Edit and change dates.

Workaround 3

Click Project settings cog > Versions > publish the Version from here, as 'undefined' text will not appear here.