Visual Studio 2008 SP1 doesn't provide any language pack prerequisite for the .NET Framework 3.5 SP1.
My research results are: it should be easy to create a custom bootstrapper package that installs a language pack. I've downloaded the Bootstrapper Manifest Generator. It's really a nice tool to create custom packages, but I don't know what are the correct parameters (e.g. reboot mode, installation time and size, install conditions, exit codes, etc.) for a language pack package.
Are there ready-to-use bootstrapper packages for .NET Language Packs?