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Thanks, this is quite helpful. Some of the technical aspects of this are a little beyond my knowledge so any laymen's terms explanation appreciated! However, those articles should help me ask the right questions of our developers to make sure we're doing every correctly.

Three of the sites are English (.co.uk, .com, .us) as well as foreign (.de, .no, etc.) - are these all seen as having duplicate content  on every site? They're hosted under the same EpiServer backend system if this helps. But I am still copying and pasting content over each site, and translating where necessary, so I'm concerned this is indexed as being large amounts of duplicate content.

Site traffic doesn't appear to be suffering but as I'm currently putting together new SEOs strategies, I want to cover this possibility.

Any advice on ensuring the sites aren't penalised appreciated!