linguist will take care of this

lib/api/projects.rb

@@ -382,13 +382,7 @@ module Gitlab
         tree = Tree.new commit.tree, user_project, ref, params[:filepath]
         not_found! "File" unless tree.try(:tree)
 
-        if tree.text?
-          encoding = Gitlab::Encode.detect_encoding(tree.data)
-          content_type encoding ? "text/plain; charset=#{encoding}" : "text/plain"
-        else
         content_type tree.mime_type
-        end
-
         present tree.data
       end