These programs:

TreePad Business Edition,
TreePad X Enterprise Server (multi-user)
TreePad X Enterprise (single-user)

all support spell checking in over twenty languages. By default, these programs install the American dictionary. Dictionaries for other languages can be downloaded from this page free of charge:

Languages

Afrikaans
American
Aussie
British
Czech
Danish
Dutch
Finnish
French
German-gt3 - ("Old" Std German)
GermanNew-gt3 - ("New" Std German)
Hungarian
Italian
Latin
Norwegian
Polish
Portuguese (Portugal)
Portuguese (Brazil)
Russian
Spanish
Swedish

Specialized dictionaries

Technical (Mathematics, statistics, computing, etc.).
Medical
Legal
King James Bible + Apocrypha
Italian Medical
Russian Scientific

Installation

To install a new dictionary, simply follow these four steps:
(1) Download the dictionary zip file to your harddisk.
(2) Open it with a zip program.
(3) Extract the .adm file (the dictionary) and copy it into the TreePad program directory.
(4) In TreePad itself, using menu/tools/configure spell check, enable the new dictionary by clicking on the associated check mark.

Please also see this screen shot: