I have a similar problem. We sell our products on the Spanish market. We need to use commas in decimals. I have used the subsitute function to replace the period with a comma. This works well when we export our records. But it doesn't work when I show the Spanish prices on the layout. The field contains a "?". I've gone into the inspector and chosen the data format of currency and set the decimal separator to "," and to ".". Both of these put the decimal separator in the wrong place.
The data is exporting correctly. But I'd like to see exactly what is going to be exported in currency format.