It depends.

Some of the components that implemented MUI is affected by the following key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\MUI\Setting\PreferredUILanguages]

The key is of type REG_MULTI_SZ which suggested that you can prepend "en-US" before your current language to see if it works for you. (Although I doubt any component that implemented MUI haven't implement en-US, which means all fallbacks after en-US is likely to be meaningless.

It depends.

Some of the components that implemented MUI is affected by the following key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\MUI\Setting\PreferredUILanguages]

The key is of type REG_MULTI_SZ which suggested that you can prepend "en-US" before your current language to see if it works for you. (Although I doubt any component that implemented MUI haven't implement en-US, which means all fallbacks after en-US is likely to be meaningless. For all the legal values of your system, see the ~\MUI\UILanguages subkey.

Since most of the Windows compoents have implemented MUI, after added/changed this key and reboot you should be able to see the event log language change for these subsystems. The setting will be read by whatever process implemented MUI on start and will not affect process that don't implement it.

Note that after you follow any of the solution here, you may experience problem when installing software that will update your performance counter. In such event please take a look at KB2480023 to fix the LCID in ~\MUI\UILanguages subkeys accordingly.