Due to player could not launch Extended Culture with BI through shortcut in Steam, here is method to do so, all of them are problematic in their own way.
1st method: In case you are lawful person....
This is lawful method as steam prefer you to use and could also use for launching with other exe with similar method.
1) Open steam library panal
2) Right click at Rome Total War Gold Edition, select "Properties".
3) Choose "General" tab
4) select "Set Launch Properties"
5) Type in space provide with...
- "-show_err -nm -mod:xc5" for Extended Cultures 5
- or "-show_err -nm -mod:xc" for Extended Cultures 4
6) Save setting
7) Launching Total War Gold Edition : Barbarian Invasion through steam launcher
2nd Method: If you as cunning as Herakles......
This method is a bit more trickery and as it is involve some modification of your main game file a bit (but not instrusive) I prefer player to do that by their own.
As you may have already know, attempt to run steam version of RomeTW-BI.exe directly would lead to game launching vanilla RomeTW.exe, not RomeTW-BI.exe. There is some trick that you could evade this by rename RomeTW-BI.exe to RomeTW.exe (which is name of vanilla RTW exe) temporary while launching game through exe directly. This would lead game to launch actual steam Barbarian Invasion. You could rename it back after you quit game.
If you want convenient way to do this and not want to repetitively do the same thing every time you could create batch file with this code inside xc5 or xc folder
rename RomeTW.exe RomeTW-Vanilla.exe
rename RomeTW-BI.exe RomeTW.exe
"RomeTW.exe" -mod:xc5 -nm -show_err
rename RomeTW.exe RomeTW-BI.exe
rename RomeTW-Vanilla.exe RomeTW.exe
This batch file would allow you to launch Extended Cultures 5 by Barbarian Invasion through batch file by temporary rename your exe file and rename them back after you push another key on CMD panal after you quit the game.
Reason why I don't include this file into installer pack is due to Lanjane consider this as modify vanilla game without player's knowledge as he prefer method which I would explain it further (4th method).
3rd Method: If you savy enough for Hermes to called you father.....
It is not impossible for you user to run Barbarian Invasion without need of renaming file or permanent modification of game but this involve hacking your own pc for some key data. It is completely legal to do it on your own computer but for us to do that as 3rd party from installer, it is not ethical at all.
Method for doing that is like this....
1) Download and Launch process explorer and find your steamID
Launch Rome: Total War. Minimize RTW and open Process Hacker. Find ROMETW.EXE in the process list and double click on it. Select the "Environment" tab then scroll down the list and you will see STEAMID with a number next to it, that is your Steam ID number.
2) created batch file with this code
set SteamAppUser=*steam-login-id* set SteamAppVersi
set SteamPath="C:\\\\\\\\\\\\\\\\Program Files (x86)\\\\\\\\\\\\\\\\Steam\\\\\\\\\\\\\\\\"
set ValvePlatformMutex="c:/program files (x86)/steam/steam.exe" set __STEAM_BOOTSTRAPPER_IC
"C:\Program Files (x86)\Steam\steamapps\common\Rome Total War Gold\RomeTW-BI.exe" -mod:xc5 -nm -show_err
Change "set SteamAppUser=" and "set SteamUser=" to your Steam login ID which could be found by either using ProcessHacker or ProcessExplorer.
Change "set SteamPath" and "set ValvePlatformMutex" if your Steam installation is located elsewhere.
Change the bottom line if your Rome: Total War: Barbarian Invasion installation is located elsewhere.
If you using this for launch Extended Cultures 4, change "-mod:xc5" to "-mod:xc"
3) Launch mod with batch file
We could not do this for you due to outsider doing so would consider as act of thief.