A500 keyboard problem ...

[DrDekker]

Do games requiring text input - output the text to screen correctly? If so, it's most probably some whacky Workbench preferences that need setting back to default.
 
Are you booting directly from Deluxe Paint - or loading from Workbench when you get the garbled text? If you're booting directly from Deluxe Paint then it's most likely a hardware fault. I'm not sure, but a faulty Denise may cause this kind of problem.
 
Might also be worth inspecting the keyboard to see if there's a key stuck down that would cause the keyboard to output alternative characters.
 
Also check the keyboard connections on the motherboard - perhaps a dodgy connection could be the problem.
 
Does the capslock LED flash at all?

[DrDekker]

As far as I'm aware you can't save any settings to the kickstart ROM - unless of course your ROM isn't an original ROM - but an EPROM with a customised kickstart.
 
I'm pretty sure it's how the preferences have been set on your WB disk - the (or 'a') previous owner may have covered the write protect hole up with sticky tape to make it writeable and altered/saved the settings.
 
The time and date will have been saved by the onboard battery backed real time clock (RTC) on the motherboard or memory expansion card (depends with mobo revision you have) - the battery is usually a rechargeable which explains why it's now held the correct time and date.

[DrDekker]

Also try booting directly from Deluxe Paint - if the text output is correct, then that will confirm that your WB preferences are at fault.