The VisualEditor UI messages feel confusing and inconsistent to me when it comes to citations, references and footnotes.
The "Cite" menu, for example. In essence, it inserts a footnote. It's not necessarily a citation or a reference. I understand the desire to have terminology that is more about functionality (citation, reference), and less about the form (footnote), but it's still a problem.
Another problem is that a "citation" is not necessarily a source reference. A citation can be a synonym of "quote" - not necessarily a source reference, but the quote itself.
Translating this to other languages complicates things even further, of course. In some languages "quote" and "cite" is the same word, which doesn't have anything to do with neither "source" nor "footnote". That word can also be confused with names of unrelated templates that already exist in that language.
One last issue I can think of now is that sometimes people will want to insert a source reference template, but not as a footnote. They can, of course, do it using the usual template insertion interface, but it seems to me that it misses the point (task T55590 comes to mind).
I don't have a silver bullet solution, but for starters, I'd suggest going over all the messages and making sure that "reference" and "citation" are used consistently. My current impression is that it's not the case. After that a terminology discussion should start, and involve the current editing communities in different languages. I believe that a reasonable baseline terminology can be found that would be translatable to all languages.