This will replace the language on the system, that is to say, you will not be able to switch the language back and forth, unless you repeat this tutorial with the proper language pack. It works on Windows 7, any version.
* NOTE * Microsoft will not supply the language packs for any language you need Ultimate or Enterprise for, therefore, you must acquire them through a windows update on ultimate, or find it through a friend or your own means. Languages not available on the Microsoft web site: Arabic, Bulgarian, Chinese simplified, Chinese traditional, Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Korean, Latvian, Lithuanian, Norwegian Bokmål, Polish, Portuguese Brazil, Portuguese Portugal, Romanian, Russian, Serbian, Slovak, Slovenian, Spanish, Swedish, Thai, Turkish, and Ukrainian * NOTE *
What You Will Need
1. Windows 7 any language, and any version
2. Command Prompt
3. Windows Language pack you wish to change it to
* Note * This may not change the entire system language, as you will be using a Language Pack (LP) as opposed to a Language Interface Pack (LIP) but I've never seen a word of Spanish on my system since
Step 1: Acquiring The Language Pack Of Choice
You will need to download a language pack to change the system language. Basically a language pack is created, and distributed by Microsoft for the ability to change the system language for whichever language you prefer.
Acquiring a language pack is simple, all you have to do is download it from Microsoft. Microsoft only distributes the languages that are available to anyone, you can find the list of available LP's ' class='bbc_url' title='External link' rel='nofollow external'>http://windows.microsoft.com/en-US/windows/downloads/languages"]Here, if you are not able to download the language you want, you will have to acquire it yourself through other means.
Step 2: Installing The Language Pack
Installing the Language pack is quite simple, you'll notice that the file you've chosen to download is in a weird .EXE file. Don't fret, what you have to do it simple, double click the file, it will create a new file for you in the same directory you saved the EXE file.
The new file you're looking for should be called: lp.cab or it might just appear as lp.
What you have to do is copy the file, and paste it into C:\ (This is just for ease of access later on)
Great! You're one more step along the way.
Step 3: Command Prompt?
That's right, we need to open up command prompt, some people may not know what that is, some might, what you need to know is how to open it!
There are several ways to open command prompt, we'll start with the fastest way.
Method 1:
1. Click on the Start button in the lower left corner.
2. Right above your mouse pointer, you should see a search box that says, Search Programs And Files, click there to make it active
3. In the newly activated search box, you should type: cmd, and it should list the program in the start menu
4. At the top of the list, you should see a black icon with cmd written next to it. Right click on the item, and select Run As Administrator
5. A new dialogue box should pop up asking if you want to authorize the use of cmd, click on Continue
Method 2:
1. Open a new window, or double click on my computer on the desktop.
2. Navigate to: C:\Windows\System 32\
3. Now scroll down until you see the programs beginning with the letter C
4. Find a program called cmd.exe or possibly just cmd
5. Right click the program and choose: Run As Administrator
You should now have a new window open up with a black background and a bit of text with it ultimately ending at a line saying: C:\Windows\System32>_ and there should be a flashing cursor.
Step 4: Changing The Language Pack
So now you have Command Prompt open, and you have your lp.cab file ready to go, all you want to do is change the system language. Well, good news, we've reached that step.
In command prompt, you need to type (Copy and paste wont work in command): dism /online /add-package /packagepath:c:\lp.cab
Remember that it needs to be copied exactly as it's seen there.
The file will now start to install, it can take up to about 10 minutes, but it shouldn't take that long. Wait for it to say Installed Successfully, then it should return to saying: C:\Windows\System32>_

That image should help out if I've lost anyone. Next we're going to have to play around in the registry to delete a key.
Open up the registry by holding down Windows Key and pressing R at the same time, and let go, a new dialogue should pop up called Run. In the new search field, type out: Regedit and then click on ok. A dialogue will pop up asking for access, click on Yes. A new window will now pop up with a lot of things you may or may not have seen before.
You should see a few hives called: HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, and HKEY_CURRENT_CONFIG.
We're going to click on the arrow next to HKEY_LOCAL_MACHINE. It will expand, and then you need to look for SYSTEM, click the arrow next to that, then find: CurrentControlSet, click the arrow next to that, under that should be Control, Click that arrow too, and find the hive called: MUI. Now under MUI you should see another called: UILanguages, click the arrow next to that and it will give you a couple folders. You should see whatever language you changed it to, and whatever language it was. For example: En-us and Es-es Right click on the language you just changed it from, and click Export and save it anywhere (This will create a back up if anything goes wrong) After it's saved, right click it again, and click delete.

Now you're main system will be in your chosen language! However we're not quite done yet, one more step
Step 5: The Startup Screen Didn't Change!
You'll notice if you restarted your computer at all that the startup screens language didn't change. Well the final step will fix that.
You'll need to open Command Prompt again, refer above if you forget how to.
Now you'll need to type: bcdboot %WinDir% /l en-us Now that line might need to be changed a little. First note that the /l is a lowercase L, and then you need to look at en-us and you will need to change that accordingly to the language you've chosen. If you don't know what the short form for the language you've chosen is, you can look at that exe file of the language pack that you downloaded way at the beginning of the tutorial, it should start out with Windows6.1 then there will be a dash, and it will list a knowledge base article, for example: kb972813 then it will list your processor bit rate x86 then it will list the language short code: en-us
So in command prompt you will need to place en-us with whatever you deciphered your language to be in short code.
That's it, all you have to do it restart the computer and it should be in a new language! Congratulations!