The 'crest' is not a crest, but in fact a Coat of Arms.

I believe it to be Saxony. The horizontal stripes would be yellow and black. The diagonal stripe is a stylised branch of the plant 'rue' (possibly laurel) and is green.



In German heraldry, coats of arms are often 'flipped' side to side, depending on how they were to be displayed.

I believe this to be a post-war German decanter made for the export market.

Regards

Chas