I did a quick search in WordPress core files, for patterns like
_e(.*nonce and didn't really find any. I also went ahead and did a search on core translation files for the word
nonce and didn't find anything at all, so my guess is that you're looking at some error message, generated by a third-party WordPress plugin or theme.
If you're lucky, the developer of that plugin or theme included translation functions (
_e(), etc.) around those strings. This means you can change them with a language file, perhaps using an editor, such as Loco Translate, or maybe using the gettext filter.
If you're really lucky, the developer or a contributor may have already created an en_GB package for the plugin/theme which uses a different word. Then you don't really need to do anything, except set the language to UK English in your site Settings.
But chances are the strings are just hard-coded in the php/js files of these third-party products. In which case, your best bet is to reach out to them and ask nicely. If it's an actively maintained product, they'll probably just reword it, because "nonce" doesn't make sense unless you're a developer, regardless of the language. If it's not maintained, your only option is to dig through the files and replace the word in all public-facing strings, which might take a while if it's a complex plugin/theme.
Hope that helps.