We are glad whenever we are weak but you are strong; and our prayer is that you may be fully restored. (NIV)
For we are glad when we are weak (unapproved) and you are really strong. And this we also pray for: your all-round strengthening and perfecting of soul. (AMP)
For we are glad, when we are weak, and ye are strong: and this also we wish, even your perfection. (KJV)