In RoboHelp, conditional build tags would be used to tag topics, or sections of text, that belonged to different languages. When generating output, you would specify which tags to include with the output.
However, I get the impression that you're seeking a means of organizing a project that would allow you to progressively translate changes or updates to the project, and then compile the project for a given language. In this case, you'd want to construct a structured FrameMaker project, and integrate this with RoboHelp. On the FrameMaker side, scripts would be used to identify and manage topics that need translation, whereas RoboHelp would compile the topics into the output format of your choice.
Can you provide more details about your project, and what you had in mind?