This page describes how to change system locale.

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Changing system locale

If the user wants to use a different language/character set (say Turkish) than the installed language of Windows (say English), it is NOT enough to go to the “Region and Language” control panel and just change the Format and add a new keyboard for the desired language. There’s an additional setting called “system locale” or “language for non-Unicode programs” that needs to be changed for the analysis engine to be able to recognize special characters of the desired language/character set. The analysis engine won’t be able to open or create files if the character set used in file/folder names is different than the language for non-Unicode programs.

References

• Changing system locale in Windows 10
• Changing system locale in Windows 7 & 8