Either give each its own data value (as is currently the case for underflow and overflow);
or have one data value holding a JSON object containing everything.
When localising, the translations will generally be available as a hash/dictionary anyway (e.g. Rails i18n) so using a single JSON object data value would be most convenient.
So that they can all be localised or tweaked invidivually.
For example:
https://github.com/airblade/stimulus-datepicker/blob/d02dbe8e9e9158bad118cbbd5ed8abba88933ef0/src/datepicker.js#L164-L166