Navigation is available in English. Just install it on an English version of Windows, all messages and screen will be displayed in (something close to) English. If it doesn't, you could go to the "Défauts" (defaults) option's tab, and set "Langue" (language) to "Anglais" (English), then click on "Ok".
There are still some problems not solved yet: for example, I didn't translate the documentation, nor I have an English version of my Web site (excepting these few words), but even if not perfect, you could try to use Navigation with these limitations.
And don't hesitate to send me a mail to have information.
Now, let's see how to install Navigation with an Internet access.
First of all, as your PC will certainly miss some DLL used by Navigation (essentially DAO and VB runtime), you'll have to install these files from http://francois.fouchet.free.fr/Navigation/Telechargement/Librairies.exe. Just run it, and give the default answer to each question. Then download Navigation's bootstrap file (NavigationAmorce.exe) from http://francois.fouchet.free.fr/Navigation/Telechargement/NavigationAmorce.exe. Again, run it and give default answer.
The installer will then start the update process (named NavigationMAJ.exe). It'll connect to my Web site, examine your current (empty) configuration, and select automatically all the needed components. You could deselect "France data"), and tick "US& data", and if useful, "IFR USA data". Then click on "Download" get and install these files.
You'll then have to start the update process again to get maps of the area you want to fly to. Click on "Map", and select, on the displayed world's map, the area you need (you could also select a country name in the right part of the window). Doing that will install maps with a pixel for 900 x 900 meters square. Repeat this step with "Details" instead of "Maps" to get a 90 x 90 m square per pixel (be aware that these information are stored on an US server often overloaded, so be patient, and repeat this operation until full completion). In any case, the first step with "Map" is sufficient, and you could download the "Detail" part at a later time.
If you want to add vector data to Navigation, do the same thing but clicking on "Vectors".
All these steps are needed only once. After, you just will have to run periodically the update process in order to get updated version of the software and data.