Try entering the game directory select language_setup.exe and select the desired language.

Italian is the third option.

EDIT: Look that too, from official game forum.

https://www.egosoft.com/support/faq/faq_answer_en.php?answer=2001&version=9

"If you have different languages installed, you can change them as follows:

Go to the game's main folder.

Open the file "lang.dat" with a text editor.

Change the stored number to the one that represents the language you want to change to:

49 - German
48 - Polish
44 - English
42 - Czech
39 - Italian
34 - Spanish
33 - French
07 - Russian

Save the changes.

If you start the game now, the starter will already be in the choosen language. If the starter only shows "TextIDNotFound"-errors you either made a mistake by changing the number or you chose a number of a language you haven't installed.

Not all of the listed languages are availabe in each game version. Some languages are provided with full text and voice translations, some only with text translations and others might be not available in your version of the game at all.

Note: X3:TC has also different executable files (.exe) which are named accordingly to the current language they start the game with (e.g. X3TC_de.exe for german or X3TC_en.exe for english). They are stored in the start menu's game folder or in the main folder if you chose the current language during installation."