linguist and web browser will take care of mimetype and encoding problem.

app/controllers/blob_controller.rb

@@ -11,16 +11,9 @@ class BlobController < ProjectResourceController
   def show
     if @tree.is_blob?
-      if @tree.text?
-        encoding = detect_encoding(@tree.data)
-        mime_type = encoding ? "text/plain; charset=#{encoding}" : "text/plain"
-      else
-        mime_type = @tree.mime_type
-      end
-
       send_data(
         @tree.data,
-        type: mime_type,
+        type: @tree.mime_type,
         disposition: 'inline',
         filename: @tree.name
       )