When are ATC FPLs mandatory (Sweden)

Dimme wrote:

A complete flight plan shall be submitted prior to operating any flight: […] Outside controlled airspace above 5 000 ft AMSL or 3 000 ft AGL whichever is higher, in accordance with VFR during darkness or IFR; […]

Does this mean that VFR/Night in uncontrolled airspace under 5000 AMSL/3000 AGL does not need an ATC FPL?

It does not!

Why did I think that is it mandatory for VFR/Night far away from the airport? Am I reading the wrong document?

VFR by night away from the vicinity of the airport does require a flight plan in all airspace classes according to SERA.5005(c). Radio communication with ATS is also required, if possible.

IFR in class G does not automatically require a flight plan according to SERA, but Sweden has chosen to use the provisions of SERA.4001(b)(3) to require a flight plan above 5000’.

Does this also mean that VFR (day) does not need an ATC FPL above 5000 AMSL/3000 AGL in class G?

Yes!

What is confusing is that before SERA there was no requirement in Sweden for night VFR flight plans in class G below 5000’. Now that there is thanks to SERA, the part about “VFR during darkness” that you quoted above could be dropped from AIP-Sweden. But having it there is strictly speaking not incorrect — only slightly confusing — so I guess it is not a priority to change the text.

Dimme wrote:

So the Swedish AIP does not fully reflect SERA?

If you take the list in ENR 1.10 1.1 as exhaustive then no, it does not fully reflect SERA.