unidentified non English, non Swedish uniform button

[btns]

I have not been able to identify this small, battered button. It is 20 mm and does not have a back mark.
A Swedish button expert has stated it is not Swedish, neither by design, nor by manufacturing.
My options are: French, Belgian or German manufacture, possibly for export.
Anyone knows what this is?

[btns]

It is a mid 19th century French colonial militia button.