sorry for the string of posts, but one last clarification --

when I initially referred to "the first dialog", I meant the "Preparing to Install..." dialog, which includes "Extracting: {my msi file}".

You are correct that SdWelcome always matched the language of the later progress dialog. However, when I tested the sample program without /passive (which would have caused the SdWelcome dialog to be skipped), all dialogs from SdWelcome (inclusive) onward were displayed in English rather than my requested language (French, in this case) when /clone_wait was used.