Hello,
“still many words are not translated” – provide screenshots of untranslated strings and we will try to help you.
The child theme should be activated, but the parent theme should be translated, read more – https://xstore.helpscoutdocs.com/article/32-child-theme
Theme Options > WooCommerce > Checkout.
If you want to change the checkout more, contact the support of WooCommerce.
Regards