1) The help for locale plugin only mentions Locale.setDefault(), but in order to avoid problems like the one reported in Jenkins issue 14703, it should also mention that allowed input can be a ISO-639 two letter language code.

2) It could be helpful to detect a non-existing Locale inside of the locale plugin and to output an error message to the user, if a locale for the entered language code is unavailable.

3) Since Windows users are used to IETF BCP 47 language tag as Locale specifiers, it would be helpful, if the locale plugin, in case a locale is not found for the current value of the "Default Language" input field, tries to find a matching locale using Locale.forLanguageTag().