Saving selected language in model

I am trying to save a chosen language in a model but want to only allow actually translated languages.
Currently I am thinking of adding a custom setting to my app with appconf and want to load that into the choices of a CharField for a model.
The two main Question I have are:

  1. Does it make sense to have a seperate settings variable where I keep track of the translations for my app or should I use the globally configured availabe languages of the website?
  2. Should I somehow force these languages into the choices attribute of CharField or do that via a form?
    The problem I encountered with the choices attribute is, that it is computed when I make migrations but it would be better if it was directly read from the settings at least at server start.