Are we sure this is a representation of a German Rifle? The French Lebel 8mm model of 1886 is also very similar. Issued to the Foriegn Legion it could indicate North Africa. French Indo China could be a possibility, the sword does seem to have Asian characteristics
I would assume that the 'deception' of the sword being a rifle would only be effective if it was seen from distance...suggesting open spaces such as deserts etc. The 'enemy' would need to see the 'rifle' to be decieved in believing that you had 'fire power' which you do not actually have.