Translate FogBugz into another language

All of the words you see displayed when using FogBugz are contained in a file called lang.asp (that's lang.php on non-Windows versions), and there exists one such file for each language in a FogBugz installation. FogBugz comes with English, German and Portugese translations, but if you're using Licensed FogBugz, you can add new languages that will then be available from the user Options page.

To add a new language such as Italian to your FogBugz installation:

Create a directory under FogBugz/website/res called it-it
Edit the FBLanguage table in the FogBugz database. Put the name of the directory you just created (it-it) into the sLangFile column on the row with the sLocaleCode of it-it.
Create your own lang.asp file and put it into the it-it directory. You can copy the file from the existing English lang.asp file. Your lang.asp can contain only a few strings if you don't want to translate all of the 2700+ strings that are in the existing lang.asp file - if a string isn't supplied for a given language, FogBugz will fall back to English.
Edit the FogBugz\Website\lang.asp file to include your new file. (e.g. at the top in the includes, add %><%)
To get the new language to show up as an option will require clearing the server-side HTML cache. You can do this by going to Settings->Clients, editing the Internal Client (or any other client), and then clicking OK. Saving any client or department clears the HTML cache.
Now users will be shown the Italian version if their FogBugz option is set to "Use Browser Format" and their browser is set to Italian, or if they explicitly choose Italian from their Options page.

Here's a sample of how you would translate a string in the lang.asp file:

Const FB_ENTER_NAME = "Enter a name."

Change it to:

Const FB_ENTER_NAME = "Introduca un nome."

Disclaimer: The above Italian translation was produced by a quick visit to Google Language Tools. It may read like "All your base are belong to us" :)