I need to update translation file only for checkout page , so how can I do that . I don't want to use translation file which is use in theme folder.
In your csv file, you should write for module:
don't change "module". just phrases and Vendor_Module. "module" here, as you understand, shows for magento where translation must be applied
PS: if you want to use translation for theme, you can do this:
where frontend/Magento/luma - path to theme