FieldWorks uses Hunspell for spell checking.
Following are dictionaries for some of the most common analysis languages. More languages can be added and if you have dictionaries you would like to share with others, please send them to Flex_DevTeam@Sil.org. To use them in Windows, download the zip file of which ever language you want and extract the contents. Save the extracted *aff and *dic files in the hunspell folders. The location is
C:\Users\<userlogin>\AppData\Roaming\hunspell (Windows Vista/7/8), or
C:\Documents and Settings\\<userlogin>\Application Data\Hunspell (XP).