I would avoid that being your main point if you’re explicitly asked to look beyond this. A lot of firms have a global element and you can imagine this is something a lot of people state to be a selling point. Equally, if it’s
Dentons’ biggest selling point, almost every application would talk about it. They’re wanting you to stand out with less obvious reasons.
It’s perhaps not that you can’t mention it at all; you could integrate it into a different point e.g., that their global nature facilitates another key selling point of that firm (from the top of my head: that it has a strong business model, is full-service, is highly ranked for banking, M&A etc). Mentioning cross-border work I’m sure would be fine so long as it’s in relation to more than just their global nature.
To supplement, you could look at recent work based in the UK, London-based clients, London initiatives (pro-bono, NextLaw, charity work etc.) and really emphasise why London is where you want to train without needing to talk too much about work outside of London.
Good luck!