IntlFAQ: Spell Checking
Your distribution contains a file called american.hash. This is a dictionary of (American) English words. By adding the hash file (and its associated encoding file) for your language of choice to the same directory as this (american.hash) dictionary, spell check can then mark those words misspelled for the language you choose. See IntlFaqChangingLanguage to set the default document language.
There is a large number of abispell packages provided for various language. You can download the package for your language from http://sourceforge.net/projects/abiword
For the Windows-Version see here: http://www.abisource.com/downloads/dictionaries/Windows/
Additionally, the unstable branch has optionally compiled in support to automatically download and install the appropriate hash file when you select the language for the currently editted text. [This is *not* currently supported in the *stable releases*; if you are using a stable releases with it enabled, please report problems to _whomever supplied the binary_.]
Note: Debian uses aspell dictionaries, dont forget to install them.