Synchronize field content (select list by languagefield)?

I use the Languafe field module. It provides a select list with all the languages Drupal knows of.

When I disable field translation, the language names are in English on all translations.
When I enable field translation, the language names are translated, but I'd have to select the desired languages for each translation by hand.

At first I thought this could/should be fixed at languagefield (#1761212: Display of language names is not translated ), but after re-thinking it, the behavior seems to be correct, because it's actually field content, no matter whether the content is provided by Drupal or the user.

So what I'd need is a synchronizing functionality.

I know there is the i18n sub-module "Synchronize translations", but this seems to only work for Content Translation (Core).

What could I do? Is there any way to synchronize the selected values among all translations?

(if Drupal would use a translated taxonomy for languages (each language would be a term), there would be no problem, but I guess this won't happen)