Hi, I am Chris a camera support tech.
The camera language being changed does happen, I had it happen before.
So here are your three options.
1. Take out the SD card then take the battery out and leave for a day or two, hopefully the camera will loose its internal residual power, it will have no access to settings info stored on the SD card so it will ask you to enter the settings again.
(This does work but not with everything but worth a try)
2. Download google translate on your phone, there is an option to translate pictures into text (its does this in real time its amazing). Set it to Japanese then Chinese until you get the right answer. You will literally watch the menus change to broken English on your screen, follow then steps till you get to the language change.
3. Find the exact number of steps needed to change it to English, (Press menu, go down three, press, select down two...etc). I have done this before, it works pretty well. You can find this either by going to a place that has the camera see it in English and then coping it on yours, or email Panasonic support and ask them for exact amounts of steps to change the language over. Eventually you will find a tech that will tell you.