Great question — answering as the UphillTech team:
For the U.K. and Canada, there's Onelink: http://amazonassociates.typepad.com/us/2017/07/monetize-your-uk-and-canada-traffic-with-onelink.html I expect that more countries eventually will be added. The bad part is that payment is made by check in the currency of each country, and most banks charge hefty fees for cashing or depositing foreign checks. Setting a high payment threshold helps.
Full answer by GeekOnTheHill: https://webmasters.stackexchange.com/a/111831 (CC BY-SA 3.0).
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