Hi,
For multi sites its an either or thing per installation, either you use host name based child sites or folder based, you cannot mix and match folder and host sites in the same installation and I would not recommend sharing the same db for 2 installations where one uses hosts and another uses folders. I mean it may work but I don't test that scenario or support it.
For multiple languages my current recommendation is to use Folder sites with related sites mode enabled so they share the same users and roles.
See Supporting Multiple Languages.
Hope it helps,
Joe