It’s not possible in Drupal 7 to define a front page per language with the core or i18n module or something. However with a little bit of code it’s still not so hard to do.
Create a custom module “alter” for example. Create the folder in “sites/all/modules/alter”. Create “alter.info”
And create a file with the name “alter.module”. And put the following code in it with your own adjustments for the right languages, default front page and the right nodes.
Enable the module in the site configuration and you’re done!