What preference settings?

Created attachment 123185 [details]
Screen capture of Preference|Language

In the Language setting there is an option to set the Locale and the date format.  Screen shot attached to demonstrate.

That dialog is for libreoffice. Dates are formatted to strings already inside libvisio, which is a separate library; it does not have access to libreoffice settings and there is currently no way to pass preferred language to it (and it would be a wrong thing to do anyway).

What I think would have to be done to support this:
1. Insert dates like actual fields, not text (i.e., insertField() with type text:date);
2. Pass description of the format (i.e., various number: properties) to insertField(), so libodfgen can create a suitable number:date-format;
3. Change libodfgen to create data formats for fields (and maybe even to handle fields at all--this might be implemented only for the text document generator now).

Step 1 should be very easy and step 2 time-consuming, but easy. The libodfgen side is a bit harder.

Could you please attach Visio file with example.
I would like to implement proper solution based on that.