Localized Formatting via FormattedNumberCellValue

[e16n]

Hello, can you please confirm that it is not currently possible to use FormattedNumberCellValue with a localized date format? I cannot find an equivalent to Excel.Range.numberFormatLocal. Therefore, I cannot reliably format my customFunction output via FormattedNumberCellValue for all locales. It must be done via Excel.RequestContext.sync which is not ideal with numerous simultaneous custom functions.

e.g., I am in the US and am returning the following from a custom function:

const fmtNumCellVal: Excel.FormattedNumberCellValue = {
  type: Excel.CellValueType.formattedNumber,
  basicValue: 45708,
  basicType: Excel.RangeValueType.double,
  numberFormat: storedShortDatePattern,
}

...where storedShortDatePattern is retrieved from application.cultureInfo.datetimeFormat.shortDatePattern
(shortDatePattern).

When my Excel-for-Web Regional Settings (File > Options) are set to 'English (United States)' (en-US; "m/d/yyyy") the static serial date is rendered and formatted properly. However, if I change my Excel-for-Web Regional Settings to 'French (France)' (fr-FR; jj/mm/aaaa'), #VALUE! is rendered in the cell.

From the documentation, it seems like this is not possible. numberFormat appears to only support a localized accessor.

Thanks.