Approach to content organization and structure

Hi, Not sure if you can help me with this as it is not so much a technical question as conceptual. The company I work for (USA) acquired a distributor located in the UK. I modified their domain to fit out brand as temporary solution but now I would like to combine both domains into 1 WP site. Most content is the same EXCEPT they spell and phrase some things differently. Not sure how to define, sort and display shared content vs content specific to each country and what can be construed as duplicate content if 2 pages exist with only a few words swapped out? Im exploring taxonomies, conditional statements, referrer redirects (if we kept UK domain name) to selectively show UK content when needed but no idea what direction to start… How would someone do this??? Thanks