A very weird language issue

Tried to solve it the whole evening ... in vain.

When I save a core language file (e.g. zh_tw.php), even without any change, it messes up the layout. The whole margin on left disappears. There are some other mess-up, too, like the "Search" word in the blank box will move half way down.

The reason I encountered this problem is that I need to amend a few translations from the original downloaded language pack plugin. But as soon as I save the amended core language file, this problem appears.

Tried saving it with ANSI, Unicode, UTF8 with Notepad. None worked.

Help please. Thanks!