I've translated the Japanese language strings for the MRZ99 to English.
I figured out the format of the LNG file, dumped the Japanese, translated all the strings using google translate, then rebuilt the file.
Some of the English is not perfect but it makes the system much more usable.
I've tested it with APP firmware version 3.070200 (installed with platform version 3.000600), other versions may not work.
If the old language file is 93627 bytes long then this will almost certainly work.
To install this, unzip the attachment mrz99english.zip and put the PF090JPJPN.LNG file on an sd card. (130905 bytes, md5sum is cb3f9cb76330704cc171e2b0acb9f6ad)
Get into testmode by holding the NAVI button (left button with Japanese writing on it) and pressing right..left..right..left..right..left and then release NAVI.
Go to the last entry on the first page (File Maintenance in Japanese) and press MENU (right button with Japanese writing on it)
This opens the file manager which is in English and fairly obvious.
Make a backup of /USER as described elsewhere on avic411.com
Look in /USER to see if there is a file named PRG.FLG
if there is, then the system uses /USER/PRG1, otherwise it uses /USER/PRG0
You can check the file versions by looking at /USER/PRGx/PF090APL.HTM (where x is 0 or 1 depending on PRG.FLG)
go to /USER/PRGx/APL/LANGDATA/
go to /SD, copy the new PF090JPJPN.LNG and paste it into LANGDATA where the old one was.
Switch off the power and when it restarts, it should be in English....
This worked for me but obviously is not 100% safe, be very careful in the file manager.
Update: I've edited the translation to make a few of the strings fit the buttons better.. mrz99English_v2.zip (130721 bytes, md5sum 7a4c582ce37f1fbca6caf0317e121ec5)