Well you could first try this:

1) 32-bit Operating Systems
If you have a 32-bit version of Windows, and additional step is required in order for The Sims 3 to use more than 2 GiB of virtual memory. You must have at least 3 GiB of RAM installed in your system before taking these steps.

For Windows Vista, Windows 7, Server 2008
Open the Command Prompt with administrative rights.
Open Start.
Open Programs.
Open Acessories.
Right-click on Command Prompt and select Run as Administrator.
Type the following and hit enter:
If you have 3 GiB of RAM installed: bcdedit /set IncreaseUserVA 2560
If you have 4 GiB of RAM installed: bcdedit /set IncreaseUserVA 3072
Close the command prompt and restart your computer.

If you have XP, here are the MTS instructions:
Windows XP, Server 2003
Open System Properties.
Right-click on My Computer and select Properties.
Select the Advanced tab.
In the Startup and Recovery area, click Settings to open the Startup and Recovery dialog.
In the System Startup area, click Edit to open the Windows boot.ini in Notepad.
Make sure to disable Word Wrap from the Format menu (you do not want a check to appear next to it).
Find the [Operating Systems] section. Each line below this header represents an operating system installed on your computer.
At the end of each line under [Operating Systems] add the following after /fastdetect (or whatever is at the end of the line):
If you have 3 GiB of RAM installed: /3GB /userva=2560
If you have 4 GiB of RAM installed: /3GB


It helped me getting rid of the annoying error 12

I had the same problem. The game always ended up installing the Dutch version.

What I did was:
1. unpacking the iso to a folder (all of the content).
2. look up in the folder setup.ini, open it and add this line after [startup]   EnableLangDlg=Y so it should look like this

[Startup]
EnableLangDlg=Y
AppName=

then save
3. run setup from the folder

With the option enabled in setup.ini you can choose the language

Hope this helps