Impossible to choose birthdate with datepicker

[svanschu]

Describe the bug
Impossible to choose birthdate with datepicker

To Reproduce
Go to profile page

Click into the date field

In this example "February 10" is not correct.
Click on February to choose the month or year

The lnaguage strings are not found
Press ESC to return and the date get changed to something wrong

Expected behavior
Possibility to enter or choose the correct date

System information (please complete the following information)

Joomla version: 3.9.25
Kunena version: 5.2.4
Kunena template name and version: Crypsis 5.2.4
Php version: 7.4.3
Database version: 5.5.5-10.3.26-MariaDB-1:10.3.26+maria~bionic

Desktop (please complete the following information):

• OS: [e.g. iOS] Ubuntu 20.04.2 LTS
• Browser [e.g. chrome, safari] FireFox
• Version [e.g. 22] 87