After you install GoldenDict, you should get some dictionaries and add them to the app.
I recommend the following in StarDict format:
http://abloz.com/huzheng/stardict-dic/babylon/french/1-Unrar them and add to a folder of your choice
2-Open GldenDict and go to Edit>Dictionaries
3-Press Add button and choose the folder of your dictionaries
4-Check "Recursive"
5-Press OK
Now you can translate!