Oh, I understand more clearly now. Thanks for the example.
In Windows 7, 8, and 10, you can have multiple languages set on the computer at the same time. You would go into the Control Panel and select the Language icon, but you might need to download the language pack from Microsoft and it could possibly depend on what version of Windows that you are using. For Windows 8 Pro and Windows 10, Windows isn't "locked" for only a particular language. You can install the language pack, where it will recognize multiple languages.
In a multi-language configured Windows computer, this would likely not be a problem, as you can set the default language to English without restarting. You would change your language preferences, by moving the default up or down. "Control Panel", "Language", "Change Your Language Preferences".
If you are sending software out to people, you can't be sure beforehand how their computer is configured. So I can see where you would want SetThreadUILanguage. But for those type of Runtime errors, you can use #ErrorStdOut (https://www.autohotkey.com/docs/commands/_ErrorStdOut.htm
). This would suppress them, so that the user doesn't see them. That's another option, depending on what you want to do. Though maybe you want users to see them or it's for yourself.