Apple - Easy way to install additional spell-check dictionaries for OS X?

Mac OS X is compatible with the aff/dic open format dictionaries.

All you need to do is to get one dictionary, and place it inside ~/Library/Spelling (you may have to create the directory).

• Get the Romanian dictionary from OpenOffice (or search for another language)
• Extract the file using The Unarchiver or rename the extension to .zip and extract it
• Move the files with the .aff and .dic extensions (ro_RO.aff and ro_RO.dic for Romanian) to your ~/Library/Spelling folder.
• Go to System Preferences > Keyboard > Text > Spelling and choose the language of your choice
• ...boom! you have system-wide spell checking :)