How can I unlock my screen when my input is in a different language?
Go to System Preferences > Accounts > Login Options and tick "Show input menu in login window" you'll then be able to change it in the screen saver password window as well

In OS X 10.7 Lion, "Accounts" is called "Users &amp; Groups".  The setting "Show input menu in login window" really ought to be active by default when plural language input sources are enabled, though.