Or is it like siwt, which I've just been told isn't pronounced with the SH ? Is the SH sound optional?
I personally pronounce this as "Shumper" and "Siwt" as "See-oot"(kind of). I'd say the whether the "si" is pronounced as "sh" will depend on dialect.
Oh dear, does this mean we're learning multiple dialects at the same time?
If there's no standardised form, what is used on official papers, like from the NHS or Welsh Assembly?
Yes, the course simplifies the dialects into North and South and accepts both answers. They have to do this because Welsh has no standardized form or pronunciation.
Ellis Vaughan, when you say "accepts" both answers, what do you mean? There is no microphone use in this course, so it won't know anything about my dialect
The course accepts written dialect answer. The pronunciation of the voice is rather neutral, but there are differences between the way dialects pronounce things.