Run import when in the import map set Setting locale en_US.
That will add a Preferred Label lang en_US.
Run another import when in the import map set Setting locale he_IL.
The Preferred Label lang en_US will be delete and new Preferred Label lang he_IL will be add.
Where did it come from:
that came from app/models/ca_data_importers.php line 2287
$t_subject->getPreferredLabelCount() > 0
if there is any Preferred Label it delete it.
it should be $t_subject->getLabelCount(TRUE,$vn_locale_id) > 0
that is count only the Label in the current import lang