HelpStudio V3:

Is it possible, to put different languages in ONE HelpStudio Project and select a certain language when calling the created chm-file from the program (same topic-IDs)?

I think, it´s not possible, but maybe you know more than me.

You can do this by using the localization features of HelpStudio (which allow you to author and build content for multiple locales in a single HelpStudio project). You would then ship a different .chm for each locale with your application and have your application call the appropriate .chm when help is requested.

Take a look at the "Developing Localized Help Systems" section of the online help for more information on the HelpStudio localization features.