Is it possible on normal European instruments to play Japanese scales like the Hirajōshi, Insen, In, Ryo, etc, without retuning? If I do have to retune, where can I find out which exact intervals are used?
You don't have to tell me exactly how many cents 12TET is off from each of these scales. An artistic judgement about whether it's 'close enough' would also be appreciated. To compare, I'll say that the Aeolian scale, I think, is close enough. It's just a little out of tune, but isn't unplayable, and it sounds recognizably Aeolian, even though the third tone in it is more than ten cents off. So, if 12TET can do these scales as well as it can do Aeolian, I'll be satisfied.
Worryingly, I've found conflicting definitions for some of these Japanese scales on European instruments. For example, the Hirajõshi scale:
Burrows gives C-E-F♯-G-B. Sachs, as well as Slonimsky, give C-D♭-F-G♭-B♭. Speed and Kostka & Payne give C-D-E♭-G-A♭. Note that all are hemitonic pentatonic scales (five note scales with one or more semitones) and are different modes of the same pattern of intervals, 2-1-4-1-4 semitones.