I've made a Regex Version, which should support international wikipedia articles once the new skin arrives for them too.

   Description: Wikipedia Vector Skin
   Example URL: https://en.wikipedia.org/wiki/Joseph_campbell
   Include pattern: ^(https?://)([a-z0-9-]*\.)wikipedia.org\/wiki/(.*)
   Redirect to: $1$2wikipedia.org/wiki/$3?useskin=vector
   Pattern type: Regular Expression
   Pattern Description: Auto Redirects to vector skin version
   Advanced Options:
       Exclude pattern: ^(https?://)([a-z0-9-]*\.)wikipedia.org\/wiki/(.*)\?