This is how I alter regional settings for Finland:
New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name Locale -Value "0000040B" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name LocaleName -Value "fi-FI" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sCountry -Value "Finland" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sCurrency -Value "€" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sDate -Value "." -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sLanguage -Value "FIN" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sLongDate -Value "dddd d. MMMM yyyy" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sShortDate -Value "d.M.yyyy" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sShortTime -Value "H.mm" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sTimeFormat -Value "H:mm:ss" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International" -Name sYearMonth -Value "MMMM yyyy" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International\Geo" -Name Nation -Value "77" -PropertyType String -Force New-ItemProperty -Path "Registry::HKEY_CURRENT_USER\Control Panel\International\Geo" -Name Name -Value "FI" -PropertyType String -Force