When was this letter being dictated? (?)

Grumbler, that sounds like Russian English. We would ask: when was this letter dictated to you?

Haha, nice, I was so close to the right answer!))

yep

Here’s a search for “when were you dictated” - even without mentioning the letter, it only brings up Russian sites: https://www.google.com/search?sxsrf=ALeKk01NpCpMIgwMyixdf4tQIVbiUkKT_g%3A1600779563696&ei=K_VpX4OLKpGAtQWfjbHgCg&q=%22when+were+you+dictated%22&oq=%22when+were+you+dictated%22&gs_lcp=CgZwc3ktYWIQAzIFCCEQqwIyBQghEKsCMgUIIRCrAjoHCAAQRxCwAzoGCAAQBxAeOgIIADoICC4QsQMQgwE6CgguEMcBEKMCEAo6BAgAEAo6BAgjECc6BQgAEJECOgQIABBDOggIABCxAxCDAToICAAQCBAHEB5Q5YETWLuaE2C8nhNoAnAAeAGAAY0CiAGsFZIBBjIuMjAuMZgBAKABAaoBB2d3cy13aXrIAQjAAQE&sclient=psy-ab&ved=0ahUKEwjDzIfK6PzrAhURQK0KHZ9GDKwQ4dUDCAw&uact=5

It's the difficult theme for all of learners, especially for new.

it only brings up Russian sites

I knew this. And that's exactly what teaches expect. This might be not natural, but correct grammatically.

OK, deleted.