The problem is that blank lines in strings get doubled (one becomes two) every time you open the language editor, and then get saved into the language file each time you save. The result for language translators was that longish strings (such as the confirmation email) keep doubling and doubling until they become hundreds of lines long.
To check if it affects you, open moodle.php of your language in a text editor and scroll down to, say, 'emailconfirmation'.
I've just fixed this bug in CVS - it seems to work OK in the tests I did on a Windows machine using Dutch files.
I'd appreciate more testing and even better, fixed checkins for languages that may have this problem. I'll be fixing anything I come across as I get time.