Feature Proposal
The locale property has been implemented for V3 in order to use it for number formatting on scale.
Nevertheless the locale can be used for dates as well, and then it could set to datefns and luxon date adapters.
I would suggest to use the locale property set at chart (or defaults) options level, as default for the date adapter (if not set on the adapter options).
Feature Use Case
With this feature, a developer can set the locale only once (in chart.options.locale or defaults.locale) instead of replicate it in several options.