First, you probably want to setup another User Account on your computer for your parents this way you can setup their browser and whatever other programs you want just for them in their account. This way you have your login account and they have theirs with Windows saving each settings separately.
You can add 2 user accounts by going to your Control Panel and looking for the icon "User Accounts." Create a login account for you, make sure you have Administrator rights, and then make an account for your parents.
Once you create a user account for your parents, login as them. Next, you'll need to install the files for the East Asian Languages. Again, in your Control Panel look for the icon "Regional & Language Options" and click that.
Then click the tab "Languages" and then in the small boxes click 'Install Files for East Asian Languages' as well as the box above if your parents need to type using right to left.
Have your Windows XP CD nearby as you will probably need it to install these extra files.
Next, in the same box, you will see a button labeled 'Details' and click that. Here you will add the keyboard of the extra languages that you added. Click the 'Add' button and select what languages you want to add.
Lastly, adjust your browser settings to reflect the main language and then log out.
Remember, do this 'after' you create a user account for your parents, then login as them and do the above. After this you can then logout and login as you and you should have everything normal again.
I hope this helps!