Juliano F. Ravasi writes:
In my experience, there are many different ways to export and import data from and to MySQL databases, and many, many of them are broken when it comes to binary data or non-ASCII text. Many hosting providers use phpMyAdmin or some variant to export MySQL databases for backup. Do not use that!
The secure way to backup databases and reimport them somewhere else is to use the command-line tools.
To export: mysqldump -uUSER -p DATABASE > FILENAME.sql
To import: mysql -uUSER -p < FILENAME.sql
I also recommend checking that the terminal locale in both systems are compatible with the 'locale' (Linux) or 'env' (other) commands. In the case of doubt, add "LANG=C LC_ALL=C" before each command to force a common locale in both systems.
That's not always secure for MediaWiki. See http://www.mediawiki.org/wiki/Manual:Backup#Character_set