ResourceManager class consisting of multiple singletons
The fact that you have "Manager" as part of the name of the class is a code smell.  This class violates the Single Responsibility Principle.

In particular, Preferences sounds like it contains user-specific data; I wouldn't call it a "resource".  It should be split into its own class.

On the other hand, Texts, getImage(), and UserInterface.titleFont appear to contain data that would be application-wide constants.  A class like this could make sense:

public class UIResources {
    public static UIResources getInstance(Locale locale) {
       …
    }

    public Image getImage(String name) {
        …
    }

    public String getText(String name) {
        …
    }

    public Font getFont(String role) {
        …
    }
}