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Countries with cans / plastic bottles deposits systems (Pfand)
(1.bp.blogspot.com)
Dark green is implemented, light green is project
Source: https://laconsignemaintenant.blogspot.com/p/la-consigne-en-europe.html (French)
I think it's too early to say if there's an impact on litter yet. It's only been a few months. I do volunteer litter picking in my area and plastic bottles are part of the waste but mostly it's other stuff, so I don't think it will make a big difference.