"It is quiet, so he says something."
Translation:Het is rustig, dus hij zegt iets.
The lack of extraneous sound -- stil
Emphasising peace and quiet -- rustig
Rustig rarely has a negative connotation, whereas stil can. (see below)
Ze is een rustig iemand. -- "She is a quiet person."
Waarom ben je zo stil? -- "Why are you being so quiet?"
Wees stil. -- "Be quiet."
Otherwise they are pretty much interchangeable in many contexts.
The main difference is word order. Dus (compare English thus) is a coordinating conjunction, i.e. the word order of the second part of the sentence is that of a main clause:
- Het is rustig, dus hij zegt iets.
Zodat (compare English so that), like all these little words ending in dat, introduces a subordinate clause. Subordinate clauses in Dutch have a different word order which is essentially the original Germanic one - SOV, i.e. the verb comes last:
- Het is rustig, zodat hij iets zegt.
In English this difference has been (almost?) completely lost because nowadays the normal word order for subordinate clauses is the same as for main clauses.
The problem is that he simply isn't a variant of hij at all. Jij is very often simplified to je, and a bit less often(?) zij is simplified to ze, but there is no general rule that this can be done with every pronoun that ends in -ij.
This is probably because je and ze do not exist as separate Dutch words, but he (or rather hè) does: hè! = hey! Or maybe it has something to do with German influence or otherwise with other dialectal variants of the pronouns: German for zij is sie, and colloquial German also has the form se corresponding to ze. But German for hij is actually er, which has no such form. Or maybe it has to do with Old or Middle Dutch: In Old Dutch, the regularity of various pronouns ending the same way didn't exist yet. Jij was gī, zij was sia, siu, and hij was hē (later hie). Therefore the various -ij endings are probably not exactly equivalent in terms of how people handle them, even today.
Just forget about he. It is not a Dutch word at all. (The Dutch word hè! doesn't mean he in English. It means hey! or what!: "Hey! He is here!" = "Hè! Hij is hier.")
- jij can be simplified to je when it is not emphasised
- zij can be simplified to ze when it is not emphasised
- hij can never be simplified to he; there is no he in Dutch.
The rest was just an explanation for the irregularity.