Trying to import the German language XML for XenForo 2.2.15 as a new language results in
This most likely happens because language XML < 2.3.0 don't contain short date formats.
Workaround
Manually create a new language and import the XML in overwrite mode afterwards
Suggested Fix
A better error messaging telling the admin that the XML file is incompatible
or
Import without setting short date formats if Skip import checks is enabled (Preferred)
Continue reading...
This most likely happens because language XML < 2.3.0 don't contain short date formats.
Workaround
Manually create a new language and import the XML in overwrite mode afterwards
Suggested Fix
A better error messaging telling the admin that the XML file is incompatible
or
Import without setting short date formats if Skip import checks is enabled (Preferred)
Continue reading...