How can I translate the checkout system? I have been translating my Commerce Kickstart site with no ease although with success until now. Have translated content, taxonomy, product fields etc, following some tutorials and Drupal own documentation. Have installed a variety of modules for localization.

But now as regarding checkout system. I'm calling checkout system all screens starting by clicking on "checkout" in shopping cart block that appear in above and right corner of Kickstart demo store.

To translate checkout system, I went in https://localize.drupal.org/translate/downloads?project=commerce and downloaded my translation (Portuguese, Brazil). Then I imported that with /admin/config/regional/translate/import. In Overview tab all the 1222 expressions (100%) are translated. In Translate tab I searched for some strings that appear in that checkout system screens, like "Payment", "Checkout complete", and indeed there are already translations in Portuguese Brazil.

In /admin/config/regional/language/configure, on Detection and selection tab I enabled URL and Session as Detection methods.

So, are there more configurations that I need to do to have checkout system translated?
In importing translation page /admin/config/regional/translate/import I have chosen "Drupal commerce"in Text group section. The process went fine, but the words to translate were indeed in Bult-in interface. So I imported the same file again but now choosing "Bult-in interface" in Text group section. Now I have checkout system translated at some degree.

I think perhaps because I installed Commerce Kickstart 2 and Drupal Commerce comes all in Built-in interface.