Is the TTS reliable?
Or is it full of mistakes? Im especially interested in the pronunciation of s and s.
Also, does Swedish have any silent letters word finally or initially?
It's far from perfect and has a rather funny melody to its pronunciation. For many sentences it gets it relatively right though.
Swedish does not have any specifically silent letters, but quite a handful of ways of spelling the sje- sound and tje- sound respectively.
S can be tricky, since our retroflex R loves to merge with the S into a tje-sound, even across a word space, which is why it'll often be heard as very similar to the english sh-sound.
Are there any specific cases you're wondering about? Or examples?
My second question was because I know Norwegian has a silent t in its definite article and its respective pronoun and silent d in the clusters ld and nd. From your answer I get that Swedish has no such cases(except for dj and gj).
Oh, yes, shouldn't have forgotten those. Word initial gj- dj- lj-, but you seem aware already. :)
In spoken Swedish, the K in words that end in -skt often becomes silent. Thus "Engelskt" will likely sound like engelst.