Have you not got an English version of Homeworld 2?
To download the english version follow these steps:
download English.zip (112 MByte);
place the files in the zip pack (EnglishSpeech.big and English.big) in your ..\homeworld2\data folder;
rename them like your original files,
(example, if you have an italian version rename them ItalianSpeech.big and Italian.big),
make a back up of your original files.

Do you have any problem with the game installation?
If you have Complex in the exe format:
Be sure you have upgraded your Homeworld 2 to version 1.1;
clear your ...\Homeworld2\Data directory from any other installed mod/addon, your ..\Homeworld2\Data directory must contain only files/directories listed below:
-Animatics
-Homeworld2.big
-Music.big
-English.big
-EnglishSpeech.big
install Complex in your Homeworld 2 installation folder;
run Complex on your desktop;
If you still have problems, try to post on the Complex forum if you have Complex in the big format:
Be sure you have upgraded your Homeworld 2 to version 1.1;
clear your ...\Homeworld2\Data directory from any other installed mod/addon, your ..\Homeworld2\Data directory must contain only files/directories listed below:
-Animatics
-Homeworld2.big
-Music.big
-English.big
-EnglishSpeech.big
copy the file Complex7x.big in your ...\Homeworld2\data installation directory (example C:\Program Files\Sierra\Homeworld2\data\Complex7x.big);
open your shortcut to Homeworld 2 (in your desktop or whatever you have it) and type -mod Complex7x.big at the end of the path (example C:\Program Files\Sierra\Homeworld2\Bin\Release\Homeworld2.exe -mod Complex7x.big or "C:\Program Files\Sierra\Homeworld2\Bin\Release\Homeworld2.exe" -mod Complex7x.big);
note the case sensitive and space sensitive nature of this command line.
If you still have problems, try to post on the Complex forum

Do you want host Complex in your web site?
follow these few rules:
be sure you have a link to www.homeworld2complex.com;
be sure your Complex download link point to: http://www.homeworld2complex.com/download/Complex7x.exe.

Other technical issues
Homeworld2 has been designed for the standard 4:3 aspect ratio display. However, you can use other any unsupported resolutions of your choosing, such as those listed below. Simply cut and paste from the text below into the Homeworld2 Complex shortcut properties,
(example C:\Program Files\Sierra\Homeworld2\Bin\Release\Homeworld2.exe -mod Complex7x.big -w 1920 -h 1440),
note the case sensitive and space sensitive nature of this command line.
You can try using this method to run in any one of the resolutions listed below or others that may not be listed;
4/3 aspect ratio:
1152x864 -w 1152 -h 864
1920x1440 -w 1920 -h 1440
2048x1536 -w 2048 -h 1536
16/10 aspect ratio:
1600x1050 -w 1600 -h 1050
1920x1200 -w 1920 -h 1200
2560x1600 -w 2560 -h 1600
Homeworld 2's default graphics quality settings are set to low. If you want to experience the full visual experience of Homeworld 2, you will need to set these values to high:
Enable V-Sync: ON
Shadows: ON
Hyperspace Quality: HIGH
Detail Geometry: ON
Damage FX LOD: HIGH
Lighting LOD: HIGH
Geometry Scaling: OFF
Also you can enable Antialiasing and Anisotropic filtering, if your video card support them:
right click with your mouse on the desktop -> properties -> settings -> advanced -> find these settings in your video card specs and change it as you need.
Please ensure you have the latest drivers before running Homeworld 2 Complex.
If you want a real game experience, remember to deactivate the NLIPS option in your Homeworld 2 gameplay options.