If you do not know how to get this, I cannot help you as I am pretty sure all the ones I know off are copyrighted.
If you on the other hand know how to find one, it is dead easy implementing the dictionary file in this keyboard.
I used the Gingerbread keyboard from LeeDroid where the & symbol has been fixed (with thanks to -snq).
Using 7-Zip or WinRAR, navigate to /system/app and open LatinIME.apk (still in 7-Zip or WinRAR)
Navigate to res/raw and replace the main.dict with your custom one.
Close up and flash the zip in recovery after making nandroid and toggling verification.
Remember that I am not responsible for any damage you may encounter flashing edited apks!
I have only tested this with Danish, but it should in theory work with any language.
If anyone know of any binary dictionaries that are free to use, you are welcome to post them in this thread.
If you want to contribute making one yourself, then follow the guidelines from google code:
You are very welcome to post them in this thread afterwards.