Diatonic is each scale you can play equal to the scales with the white keys. So any other mode that can be fitted in a same pattern of 5 whole tone steps and 2 half tone steps arranged in the same way as the white keys of a keyboard is diatonic.
This means: all scales like wwhwwwh, whwwwhw, hwwwhww, wwwhwwh, wwhwwhw, whwwhww, hwwhwww, will always have a pattern ww and www if they have a range more than an octave.
As we see the pitch doesn't play a role and neither the root tone of the scale.
Examples:
All major scales and all natural minor scales,
all church modes without accidentals and
all Greek modes build on 5 w and 2 half steps as described above.
All intervals derived from this scales are diatonic intervals.
So far what I know without looking consulting other sources.
N.B.
The Greeks had diatonic scales built of 2 tetrachords downstep like e,d,c,b,a,g,f,e and as we can read in wiki they also had "chromatic scales" with other half steps and "enharmonic scales" with quarter steps.
https://en.wikipedia.org/wiki/Musical_system_of_ancient_Greece
Mind that there are 2 definitions of "diatonic scale":
a) the traditional classical definition
b) the modern extended definition
I'm posting here a google translation of the German wiki site, which is more detailed than her English sister:
The root tone series c-d-e-f-g-a-h corresponds to the white keys of the keyboard. These are the notes of the C major scale.
Diatonic scales are usually seven-degrees (heptatonic) scales, dividing the octave space into five whole and two semitones. They differ from non-ionic ladders by the following necessary characteristics:
All scale steps are derived from different root tones, which is externally reflected in that their names all begin with different letters.Between adjacent stages, there are no excessive or reduced intervals.For example:
The "classical" diatonic scales (major, minor, and church modes) additionally fulfill the condition that they can be composed (by adding a further whole-tone step) of two diatonic tetrachords. Also, the tones of these scales can be obtained by fifth layering.
The seven pitches of any diatonic scale can also be obtained by using a chain of six perfect fifths.
Any sequence of seven successive natural notes, such as C–D–E–F–G–A–B, and any transposition thereof, is a diatonic scale.
In extension of this original strict definition, sometimes even those scales are called diatonic which merely fulfill the condition of subdividing the octave into five whole and two semitones. Examples are the acoustic and the altered scale.
In addition, according to the present understanding, also scales can be regarded as diatonic, containing less than seven tones, such as. As the anhemitonic-pentatonic ladders, which divide the octave space in three whole steps and two thirds.
The diatonic scales in the narrower sense ("classical" diatonic scales) also include the church tones and the modal scales that today draw on them.
In the broader sense these scales are also diatonic:
the melodic minor scale upwards
the altered scale used mainly in jazz
the acoustic scale
the anhemitonic-pentatonic ladders
Not diatonic scales
These scales are not diatonic or not completely diatonic:
the harmonic minor scale, as it contains an excessive second (hiatus)
the gypsy ladders, because they contain excessive seconds (hiatus)
the whole-tone scale, since the last whole-tone step needed to reach the octave is in reality a diminished third (in the notation ais-c from c)
the chromatic scale
the modes with limited transposition possibilities of Olivier Messiaen
My conclusion:
Now deriving chords and intervals of these scales in a broader sense (extended definition) will lead to a confusion that we better talk about diatonic chords and intervals derived from the scales defined in the classical meaning.
The following list e.g. counts all 3 kind of minor scales to the diatonic scales: