Download the installation file from the Download Page or with this link.
Multi-Language is packaged in a VSIX file, which is a special format for installing Visual Studio Extensions.
To install Multi-Language, either:
The VSIX Installer will open and show a progress bar for a short period. After this it will show a list of the possible products, with which the project can be used.
It will look something like the following screen shot, but will probably not show so many products.
In this case, four different versions of Visual Studio are installed on the same machine