Any Ukrainian Immersion articles?
Has anyone successfully uploaded any? Does anyone know the language code to use to upload them?
Yes, I have seen the Ukrainian Immersion section. Looks like there is a total of 14 articles uploaded so far. I think the two-letter code you are asking about is uk}, but that is only if you want to translate an article from a language to Ukrainian. If you want to translate a Ukrainian language article to English, you would upload the Ukrainian article and use the code en}.
If you do have access to the Immersion section from one of the first five languages (German, French, Spanish, Portuguese and Italian) then you can trick your way into the Ukrainian Immersion section (if you don't have access to Immersion, there is an add-on for Google Chrome that opens that back up, found here - https://www.duolingo.com/comment/17576074). Starting from a screen in one of those five languages, open Immersion in a new tab. Before that Immersion tab loads, change the language to Ukrainian. The second tab should load with a list of Ukrainian immersion articles.
If not, here are some direct links.