There is lack of in-depth documentation about "Restricted Interfaces for Translation" permission. You need to give two kinds of permissions in order to access specific list with no access to your subsite.
Give "Restricted Interfaces for Translation" to user/group permissions on subsite.
Stop inheriting permissions on your list and give unique permissions with "Contribute" permission to user/group.
Query 1: what does open list and folders mean?
"Open permission" inside "Restricted Interfaces for Translation" says that it allows users to open a Web site, list, or folder in order to access items inside that container. That means, first of all you need to give "Restricted Interfaces for Translation" permission on subsite in order to access the list items& then "Contribute" permission on list will actually allow you to access the items.
If you will give only "Contribute" permission to user/group on list without "Restricted Interfaces for Translation" permission on subsite, Then you will get "
Unable to communicate with server" error while updating the item & "
Access denied. You do not have permission to perform this action or access this resource." error while ading the item.
Query 2: what does use remote interfaces mean? could this mean that users with "Restricted Interfaces for Translation" can still view the list items using the list api
REST API, Web Services, Client Object Model Application (Windows applications), SharePoint designer these are remote interfaces which allows user to access sharepoint resources remotely.
"Restricted Interfaces for Translation" on site doesn't allow users to access items from all lists/libraries. But User can able to view all lists/libraries properties by remote interface (like REST API, Web Services).
For verification, I entered below rest url on browser and checked (First give above mentioned permissions on sub site and your list & try below api on another list on which user has not any permissions)
SiteUrl/_api/web/lists/getByTitle('List Name of no user permission')
above api will give you list properties.
SiteUrl/_api/web/lists/getByTitle('List Name of no user permission')/items
above api will not give any response of items.
Now regarding to sharepoint designer, SPD doesn't allow user to open site/list in designer who having only Restricted Interfaces for Translation permissions .
So, as per my experience, Only "Restricted Interfaces for Translation" permissions on site doesn't allow user to access all lists & list items. For accessing the list items user also needs "Contribute" permissions on list.