Thank you all for the suggestions.As a recap, the configuration file which had been altered by mistake was ~/.config/user-dirs.dirs. Problem solved.
Source: https://sites.google.com/site/installationubuntu/tweaking-ubuntu/change-the-location-of-subfolders-in-your-home-partition
It seems the problem did not arise from mistakenly renaming but from mistakenly moving the folder around.
