Re: "a mechanism where knowledge domain concepts from the source wiki could be mapped to identical concepts on the target wiki"
I'm not familiar with how Content Translation handles this, but I assumed it was simply via checking Wikidata's interwiki links? I believe that is how the toolforge translate tool works (you specify a source-article, and it finds equivalent in-article links in the target language).
There's also phab:T121470 to consider ("Central Global Repository for Templates, Lua modules, and Gadgets") [that's a more detailed duplicate-task of a much older task].