Let a mac application run in default language as you like

To do that, just use ‘defaults’ command.

The usages is simply:

default [command] [domain] [attribute] [value]

If I want to change the default language of com.apple.mail to be English while the whole system is in Chinese, just type in terminal:

defaults write com.apple.mail AppleLanguages ‘(“en”, “zh”)’

It will search for English language pack first, then Chinese.