The issue you have run into looks like it may be identified here: https://www.drupal.org/node/1183440. I walked through this issue queue and was able to get my feed processor to specify the language it was importing. The comment #193 was particularly useful. I'll elaborate on his directions a little bit.
For the record, this patch applies only to the feeds module, but you will need to have Feeds Entity Translation installed as well (which you probably already do).
drush dis feeds -y
rm -rf feeds
- remove feeds directory entirely
git-pull the feeds repo and checkout older commit:
git clone --branch 7.x-2.x http://git.drupal.org/project/feeds.git
cd feeds
git checkout 006234fc3cc859e4fec0cb261675577efcf389b8
enable all feeds modules that were disabled from step 1:
drush en feeds, feeds_ui, feeds_tamper, feeds_tamper_ui, feeds_et, feeds_ex -y
patch feeds:
wget https://www.drupal.org/files/issues/feeds-field_translations-1183440-191.patch
git apply < feeds-field_translations-1183440-191.patch
confirm patch by building new feed. you should see a language option under the processor settings.
There is a little bit of work to do on this patch before it can be incorporated in the Feeds trunk, but I'm hopeful it will be in place within a few months.