Instead of writing into the global domain, you could set the preference only for the specific application, then it will apply to that application only…

eg.
defaults write com.apple.mail AppleLanguages '("jp", "en-US")'

I'm probably missing something, but why not enable "Show input menu in menubar" in the International preference pane (under the "Input Menu" tab)? Then you can switch languages to your heart's content by choosing the appropriate flag.

In the input menu you can change the keyboard lay-out, not the language in which applications (including the Finder) will be launched.

This is brilliant and fast.

Very useful in particular for mail as the language encoding can be switched on the fly via the input menu and it will look like things are well. However the actual message encoding does not properly move to SJIS unless the program is running in Japanese and the message will likely come over to the recipient looking garbled and not in Japanese at all.

Good work. I'm using it now!

Very good. I've copied your droplet script and changed it to run in German. Excellent!

Something from my cut-and-paste of this hint nuked my user account. I suspect I gave the Terminal a bad language code and now, it seems, launch services are hosed. My desktop image and doc work but menubar and applications (including Finder) will not launch; also, I cannot log out.

Can anyone spare a tip on how can I administer terminal commands from another user account so I can try to fix this?

If you have a second user account that you can login to, you should be able to open up the terminal and type su username in order to switch to that user. For example, if I'm logged in with a_user and I want to switch to b_user, I could type su b_user and then b_user's password and then I would be logged into b_user's shell. From there I can run whatever program I want as b_user.

I can't actually test this right now (I don't have a Mac at work), but I believe it should work.

Thanks for the fix!

I have created several accounts on my system and tried this hint 3 time. Each time the account becomes useless; i.e., it will not launch the menu bar or finder (or any other app). There does not seem to be a reset back to "en" after the error. Maybe it is something unique about my installation but this is the first symptom, if so.

I do not recommend this hint unless you are a geek god (no offense meant to the kind person that contributed the hint).

defaults write -g AppleLanguages -array en

defaults write -g AppleLanguages -array ja

Lotus Notes, the bane of our lives, is not capable of using Japanese as long as the OS isn't switched to Japanese, even if you disable the English.lproj and leave only the Japanese one in. It will mangle all the Japanese characters. My workaround was to switch the Language in the System Prefs, kill the Dock, launch Notes.app via the dock (and it thinks now it's in a Japanese system) and once Notes is running I switch back to English and kill the Dock again.

I used your method to try to automate that process, but for some reason switching languages via the command line is missing something compared to the System Preferences, because Notes will just refuse to "think" it's on a Japanese OS, it will mangle all the Japanese. Back to manual, I guess.

I really hope I'll never meet any of the Lotus Notes developers in a dark alley...

Anyway thanks for this hint.

i have been looking for a way to do this for a while. your applescript seems to need one to drop something onto it to change the language?

how could i make an applescript that just changes the languge?
i would like to have one to switch from japanese to english?
and one to switch from english to japanese...

im on leopard now but that shouldnt matter right?

im afraid of screwing up my user account so i dont wanna try to edit this applescript myself....

thanks!