A solution would be to enable MultiTenancy and to create one tenant per culture (keeping the default site with default culture).
You configure one tenant for each domain and in the Settings of a tenant, you set the correct culture.
You can use the same database (using a Prefix when you configure the tenant) or separate one database by domain.
You can have the same Theme or select one by domain.
It's bit more complicated to administrate because you have to explicitly enable the modules on each tenant and to repeat the same configuration you already set in the default site (widgets, users, ...).
You also have to switch between the admin but this way, you have more control on your domains and contents by culture.
An annoying problem is that the admin of a tenant is translated in the language that you set in configuration.
That's why I made this suggestion in Culture Picker Module discussions: http://orchardculturepicker.codeplex.com/discussions/266705 : Allow to specify the culture used