An interface administrator has different rights than a regular administrator. Before August 27, 2018, administrators could edit JS and CSS pages. Now, the interface administrator permission is needed to edit those pages.
Requests should be made at Wiktionary:Requests for permissions#Requests for interface administrator. The user right will be given by bureaucrats. This user right should not be held for longer than necessary, and bureaucrats should always add an expiry date to the rights, even for themselves.