To add this to your website, you'll need to obtain the code from Google - go to https://translate.google.com/manager/website/
and you will need to create an account in order to obtain the code.
There are a few options for configuration - Step 2 would be the main one to look at, which allows you to change the look of the drop down selector and to hand-pick the languages you want shown. Or you can leave all these as defaults.
You will need to copy the code generated in the Add Plugin step into your website. The place you want to paste it is the 'Extra HTML tags' box.
Log into Website Manager and go to Preferences>Content to find the box. Make sure when you paste the code in that you don't delete any existing code from the box - doing so may cause things to break, such as the fonts on your website. Remember to hit the Save button when you're done.
If you're unsure you can contact us