Private Swap - France
The red lion is the official ensign for ships registered in Luxembourg. It is used for river and sea shipping, as well as for aviation. This flag is based on the Coat of arms of Luxembourg and is used as the ensign to avoid the possibility of Luxembourg's ensign being confused for that of the Netherlands. Ten white and blue stripes serve as the field for a red lion with a yellow tongue and crown. (source)
Thank you Marie!