Edit /etc/default/locale and set the contents to:
LANG="nl_NL.UTF-8"
You can check which locales you currently have generated using:
locale -a
You can generate more by editing /etc/locale.gen and uncommenting the lines for the locales that you want to enable. Then you can generate them by running the command:
locale-gen
You can find a list of supported locales in /usr/share/i18n/SUPPORTED
There is more information available on the Debian wiki.
First, before I get to the real answer, I'm going to explain why I'm not directly answering your question. Sure, you could likely write up some script that would do what you wanted. It would solve this problem, but would do nothing at all to solve the dozens of other potential problems you'll run into sooner or later.
So with that, here's the real answer...
You've run afoul of the most important rule when using AWS for anything serious: the web console is for inspection only, not making changes. It is just plain too easy to forget steps, mess things up, terminate the wrong instance, etc. when using the web console.
When creating instances, you and your staff should only be using one of the many technologies AWS provides to create resources in a controlled, reliable, repeatable manner.
At the very least, get to know the AWS Powershell Tools. After you've familiarized yourseif with them, create, publish, and distribute to your staff a standard method of interacting with AWS.
Ideally, you would create a wrapper around their API, which your staff can use, which would force them to provide relevant tag info before instance creation.
Additionally, ensure that all of your staff are using their own IAM user. Do not, under any circumstances, permit anyone other than the account owner have the account root credentials - even that person should only use those credentials for the bare minimum of tasks, instead using an IAM user as well.
Best Answer
This set of instructions I found for Windows 7 on windows.microsoft.com seems to work:
Open Region and Language by clicking the Start button, clicking Control Panel, clicking Clock, Language, and Region, and then clicking Region and Language.
Click the Administrative tab, and then, under Language for non-Unicode programs, click Change system locale. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
Select the language, and then click OK.
To restart your computer, click Restart now.