It seems to me that the "sh" sounds in "varsågod" and in "kyckling" I now came across are different both from the English one (as in eg "shell") and from each other. Is it true and if so, how do you make them sound differently (different position of the tongue or something?) and are there any rules as to when to use either? Tack.
They are slightly different but very close.
The sound in varsågod is [ʂ]. It is made by the tongue bending backwards in the mouth, a so called retroflex consonant (retro-flex = back-bent).
The sound in kyckling is [ɕ]. It is made similarly to English sh but there should be more contact between the tongue and the roof of the mouth. In the English sound, only the tip of your tongue touches the roof of the mouth behind your teeth, but for [ɕ] (tj-sound) it is a larger area of the front part of your tongue.
The first one (1) is always in the combination rs or for some Northern dialects also for sj but that’s a minority. The second one (2) is the tj sound in tjej and the k before front vowels as in kyckling.
There are some words like lunch, dusch and beige where the sound in the end in many dialects is either (1) or (2), I’m not actually sure which one it is because I use neither in my dialect for these words. I use the sj-sound [ɧ]. :)
These are very small differences and there is no risk at all for misunderstanding, but since you asked you get the long answer. :)
And it's as clear and detailed an answer as I could have wished for! Tack så mycket!