>I use the german VFP6 and installed Servicepack 4 (German).
>With SP3 I was able to switch the language of the develping environment to English, with deleted or renaming the vfp6rdeu.dll. After installing SP4 I can rename the dll, but the language is still German.
>What can I do?

There's a command line switch (-D) that allows you to designate which RT library to use. Click here for details.