In which dictionary exactly do words added with Right mouse click -> Spelling -> 'Typo: Save 'foo' to dictionary' go? How to remove them from there?
If you want remove a word from the dictionary you can go to:
Settings->Editor->Spelling
Now you should see a window with two tabs, Accepted Words and Dictionaries.
Click on the first one (Accepted Words) and click on the word that you want remove.
After this press on minus icon on the right of the page to remove the word.