There have been several reports of people finding their hard disks more full than they expected. The following are known causes of disk filling up and how to solve them:
1. MacAlly's iShock older driver created extremely large logfiles, and its support page explaining how to fix the issue:
2. Hard disk capacity knowledgebase article:
3. Incomplete backups with Carbon Copy Cloner, and locating the file in the /Volumes/ directory.
This is explained on Bombich's website:
4. Incomplete burns with the Finder. I don't know where the temporary files are stored with this. Maybe someone can help here?
5. Using a not up to date version of an anti-virus program. Norton Anti-Virus fixes 9.0.1 fixes an issue whereby a space filling file called "spacesuckingfile.xxxxxx" can fill your system. This is documented on Symantec's website.
If any of these do not appear to solve your disk filling up problem, find out the source of your disk space usage by using one of these utilities if Spotlight and Find File can't find the disk filling file:
Omni Disk Sweeper
And only delete known files that won't affect your system's ability to operate. If you have a question, ask someone here on discussions which files are safe to delete.
If you didn't delete the foreign languages when you initially installed your system, you can do so by deleting the non-English languages with Monolingual.