Regarding the Primary Dictionary
option, I just had a look at the K4 manuals and according to manual there's a Dictionaries
option that lets you choose the primary dictionary.
Kindle 4 Touch
To go to the Settings page, select Settings from the Home screen menu. Use the Next page ► and Previous Page ◄ buttons to view all the options. The available settings are:
Dictionaries: Lets you choose which of the installed dictionaries to use for word lookups.
To go to the Settings page, tap the Menu button from the Home screen, then tap Settings from the displayed menu. The available settings are:
Dictionaries: Lets you select the default dictionary.
Out of curiosity, are the manuals incorrect, are these options only available on registered K4s or do they exist but don't work?