[SamuelAdams]

Depends on the requirements. I've had many internal-only applications only require one language: English. At that point you can hard code many things, which skips the loading other files, checking different languages, etc.

[OJFord]

I'd still rather the exact wording isn't in code, personally:

    get_msg('fail_add_address')

vs.

    'I\'m sorry, we\'ve been unable to add the address %s at this time,' \
    ' please try again later.'

(... but that's an ideal I have without ever having worked with it, so what do I know, and ymmv, etc.)