PyGObject: cell_data_func or own Renderer for date column?

[<c buhtz posteo jp>]

I want to have a date column in a Gtk.ListView. The field in the model
is a real "datetime.date". Based on that the content of the column
could display this:

  "2018-05-07"
  "2 days ago"
  "this week"
  "7th May"
  "7. Mai '18"

This is all based on the same "datetime.date" instance. The user decide
how to display. So I need maximum flexibility.

A cell_data_function is an option here to implement this. Is it a good
choice?

What is about deriving from Gtk.CellRendererText?
But I don't see how to do this. May I only overload the render()
function? But how can I read from datetime.date object and convert it
to a string?