Steps to reproduce

1. Add a Date Time Picker custom field and associate it with the Create Issue Screen
2. Change your language to German
3. Create an issue
4. Click on the date picker for Due Date
5. Try to change to next month by hovering on the next month button
6. The description of the button will show at the bottom of the date picker: Nächst. Monat (Festhalten für Schnellauswahl)
7. The text is too long that the date picker resize
8. When it resize to be longer, my mouse cursor is not hovering the button anymore so the description text change and the date picker resize to be smaller again.
9. This create a loop resize effect
10. Click on the date time picker for the custom field created
11. Similar observation encountered when attempt to click on the minute area

Workaround
This workaround is applied to JIRA Server only. JIRA Cloud does not support the customisation of source files. See Restricted functions in JIRA Cloud applications.

1. Shutdown JIRA
2. Edit <jira-install>\atlassian-jira\includes\lib\calendar\lang\calendar-de-min.js so that it will have a shorter description text
3. Restart JIRA

JIRA Cloud Workaround

Use English language pack instead of German.

Additional Information

• This behaviour is consistent throughout the Chrome and Internet Explorer, but Firefox seems to be not affected by this, it is able to handle the long description by creating a new line.

• For JIRA Cloud, tested and verified that this is affecting on Firefox.