Hi, Adal! Try this (for Office 16), although I'm not sure about es-es:
Code:
Sub Office_Prefd_Lang_Esp()
CreateObject("WScript.Shell").RegWrite "HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\LanguageResources\PreferredEditingLanguage", "es-es", "REG_SZ"
End Sub
After running the code, restart Word.