My understanding would be that locale should dictate numerical formatting. But one could argue the opposite and also be right.
From "man setlocale":
LC_ALL All of the locale
LC_ADDRESS Formatting of addresses and
geography-related items (*)
LC_COLLATE String collation
LC_CTYPE Character classification
LC_IDENTIFICATION Metadata describing the locale (*)
LC_MEASUREMENT Settings related to measurements
(metric versus US customary) (*)
LC_MESSAGES Localizable natural-language messages
LC_MONETARY Formatting of monetary values
LC_NAME Formatting of salutations for persons (*)
LC_NUMERIC Formatting of nonmonetary numeric values
LC_PAPER Settings related to the standard paper size (*)
LC_TELEPHONE Formats to be used with telephone services (*)
LC_TIME Formatting of date and time valuesI've got GNOME set up in English, but my region to be the Netherlands. It will helpfully display local dates, but that also results in the month names being in Dutch.
If by "local dates" dates you mean the format rather than timezone then LC_TIME=en_DK will give you English text with RFC3339 YYYY-MM-DD formatting.