Because the checkout page is Shopify element so we do not support this, and you can do it yourself from Shopify admin
You can manage it in the theme editor by this way:
Shopify admin > Online Store > Theme > Action > Edit language.
OR Edit the language by going ahead to Shopify admin > Settings > Checkout > Manage Checkout language.
Click on checkout & system
Then it will show you all checkout sections showing on your website for you could easily check and edit them manually.
From there, if you want to translate your whole checkout or just part of it, you could also create your own check-out language OR translate/edit checkout fields individually in Shopify admin. For more details, please click here.
Although we do not support to translate the check-out page yet, but our developer has been trying to research the checkout.liquid asset and find other solutions to get it supported in as soon as possible. For sure, we will keep you updated once it's available.
NOTE: The checkout.liquid asset is available to Shopify Plus merchants only. If your store isn't on Shopify Plus, then you can customize your checkout pages in the theme editor as the instruction above.
If you need some more help, please feel free to contact us via live chat or email us at firstname.lastname@example.org