Fix unable to download coupon report in non-english languages.
Fix unable to download coupon report in non-english languages.

field_names list have translated values but upon removing we are using
untranslated strings.

LEARNER-4648

edx/ecommerce,eduNEXT/edunext-ecommerce,edx/ecommerce,edx/ecommerce,edx/ecommerce,eduNEXT/edunext-ecommerce,eduNEXT/edunext-ecommerce,eduNEXT/edunext-ecommerce