my solution sometimes says -1400 is a leap year

Ignoring that this is very blatantly a duplicate and should never have been approved, what the hell -

A variation of determining leap years, assuming only integers are used and years can be negative and positive.

That reads like nonsense. What. Are. You. Talking. About?
You could start with "this is" or like, "hi", or something.
integers? as opposed to what? bananas?

Also the basic rule for validating a leap year are as follows

plural. there's more than one rule.

There are a few assumptions we will accept the year 0

how even english

Whilst

if you're going to use fancy words then the rest of the text needs to not be broken.

where's the unpublish button?

if you get an error message, read it.

Weird. Failed Python test even on PC it works correct as per task. Test failed only with 300. It divides by 4 it means it should be 365 days but it shows me 366 should be instead. ok. But why other attempts failed.

javascript tests are wrong for the negative century years.

Can you elaborate on this issue?

How many days are there in the year 100 / -100 / 400 / -400 respectively?

Exception: Century years are NOT leap years UNLESS they can be evenly divided by 400.

javascript tests are wrong for the negative century years.

Well, try asking yourself: What is the value of "f" in each loop?.

You can use console.log for the answer. From here, you should know why.

Very cool, but I feel like understanding the wording and the problem itself in this kata is a kata of its own

Because it's not an empty array or null. The tests are fine.

python: i have encountered this issue where if the result is for instance 15.5 it sometimes averages to 16, sometimes to 15 without modifying the code like i would just hit "attempt" multiple times and i would sometimes get 1 failed test, then i would get 17 failed tests, then i would get all the tests passed.

In the 100 random tests some of the tests require [0,0] instead of an empty array, which is why I can't pass