The checkout page can be translated as long as you are using the responsive checkout.
It works just like the translation of your own content, check the Knowledge base for detailed information on how to translate your page or follow this short overview:
Translating the checkout page
Navigate to the "Theme Translations" section in langify and choose your main theme.
You can now either import an existing theme translation
or translate manually by choosing the checkout template and filling in the translation.
As before the progress bar on the right turns green if you proceed.
A page with two columns should open, the left column contains the original content and can't be altered.
Enter your translation in the right column and save your progress.
Unfortunately the product name and custom payment/shipping info cannot be translated on the checkout page and will always show up in your base language.
We hope this tutorial was of use, if you are still struggling with your translations or have encountered any problems which we haven't discussed here feel free to contact us.