product_commerce schema declares 'language' field, while
commerce_product entity info doesn't.
This leads bad things to happen, like described in this issue:
(The author tells about his problem with nodes, while I can confirm this for commerce_products).
For example if a
commerce_product entity is created inside Rules, there is no way to set language value which results to EMPTY value for
language field in the DB.
To fix this I simply added appropriate declaration in