I followed the steps indicated in the help: File > Options > Corrections > Spelling. I downloaded both the English gb dictionary and the English us dictionary. The download completed without error. I then used the Select button to select the gb dictionary and click Apply.
The result: all the words are underlined. So, to me, Scrivener seems to be able to find the dictionary (otherwise I would have an error message), but this dictionary, which I just downloaded, is empty.
Could you help?