The Edinburgh International Festival closes with the annual fireworks concert tonight, an event whose cheerful populism is the opposite pole to an admirable internationalism that mounts plays in Polish, Arabic, Bosnian and Farsi, operas in Polish and Russian. The latter were brought from St Petersburg by the Mariinsky Opera and Orchestra and its unstoppable director, Valery Gergiev.

Before them I caught a work intermediate between genres and languages. Ruhe (Rest), presented by Antwerp’s Muziektheater Transparant with Collegium Vocale Gent, could be seen either as a play (in English) with music (sung in German) or a concert with surprising interventions by actors. The audience were part of the show, admitted to the Hub space only at the last minute. A concentric arrangement of 200 different chairs was the mise en scène, and on 12 of these Collegium men stood and sang Schubert part songs, very euphoniously. This is music traditionally left to amateurs, and it was a shock to discover how raptly felicitous Schubert’s writing is. A greater one was when the actress Carly Wijs stood on a chair to deliver a chatty monologue in which her Dutch character justifies collaborating with the Nazis. More part songs, then the thug-like Dirk Roofthooft did the same, with much haranguing of the audience, constrained by politeness to go along with him, or at least not be hostile.

The texts are from interviews with unrepentant ex-SS members collected by the Dutch artists Hans Sleutelaar and Armando. The director Josse De Pauw rounds off his show with Annelies Van Parys’s Ligeti-ish, chromatically sinking Ruhe, a part song using words from one of Schubert’s, as if to cap romantic innocence with modernist queasiness. De Pauw seems to be saying we must all share responsibility for the characters’ ethical choices: they were “ordinary people” like us. But it was impossible not to feel he also held Schubert responsible. It is evidently no longer enough to blame Wagner for Nazism; any Austro-German composer will do. One wonders which unsuspecting composer of today will be called to account for atrocities committed 100 years from now.

What Gergiev’s theatre offered was more conservative if rather more explosive. Having conducted a Prokofiev symphony-cycle with the London Symphony Orchestra earlier in the festival, he undertook a concert performance of Act III of the same composer’s Semyon Kotko with Rachmaninov’s Aleko at Usher Hall; a staging of Szymanowski’s King Roger at the Festival Theatre; and the British premiere there of Rodion Shchedrin’s 2002 “opera for the concert stage”, The Enchanted Wanderer. During this re-creative frenzy (absolutely habitual for him) he was doubtless exercised by political ructions in his native Ossetia.

The festival’s theme this year is, uncannily, the shifting of political boundaries, and this explains the unusual conjunction of Rachmaninov’s student one-acter about those non-respecters of borders, gypsies, and the isolated act (of five) from Prokofiev’s 1940 Soviet opera about German and Cossack resistances to Bolshevik rule in the Ukraine of 1918. The first, based on a poem by Pushkin, was a simple entertainment: a tale of bloody revenge exacted on his wife and her gypsy lover by the tormented, eponymous baritone — the strapping-voiced Evgeny Nikitin — and a reminiscence of Puccini’s vengeful one-acter Il Tabarro, recently heard at the Proms. Rachmaninov’s score has nothing like the sly seductiveness of Puccini’s, though it is similarly preoccupied with creating atmosphere, and Gergiev splendidly brought out the orchestral colours — haunting flutes in the opening gypsy chorus, Glinka-esque string wildness for the men’s dance, a disconsolate horn for the tragic finale. The singers fell effortlessly into moody poses and gave their all with mighty Russian readiness.

Semyon Kotko was a vivid contrast: a cast of 20, a rapid, quasi-cinematic unfolding, furiously inventive orchestration, and a steady rise in tension to the overwhelming close. It did not matter that we were plunged in medias res. The depiction of love and terror in wartime is fiercely delineated, and so much drama is packed into this act that I shudder to contemplate the force of the whole opera. Though Prokofiev is intent on keeping things moving, he gives impassioned monologues both to the demobbed soldier Semyon (Victor Lutsiuk) and the village girl Lyubka (Irina Loskutova), whose grief for her hanged lover takes the form of a savagely insistent six-note figure. The thrilling inevitability with which this returns at the end to dominate the tutti is the kind of ploy that makes the art of opera special.

Gergiev barely had time to sleep before impelling us through another tempestuous operatic experience, Szymanowski’s lush, ecstatic, powerfully condensed treatment of Euripides’ Bacchae story. Mariusz Trelinski’s production added a silent preamble in which we were faced by rows of empty chairs, and I had a bad memory of Ruhe. They are gradually occupied by worshippers in a cathedral, and the music begins. It is a brilliantly original score, for all that it actively evokes Debussy, and one would be sufficiently transported if one sat with eyes shut. Boris Kudlicka’s sets were ravishing but apt to confuse: the Greek amphitheatre of Act III was a ghostly hospital ward. Andrzej Dobber as Roger was impressive, the tenor Pavla Tolstoy, a dazzling white-clad Shepherd/Dionysus, even more so. Elzbieta Szmytka as Queen Roxana had much erotic writhing to do. The closing sunburst, when Roger definitively overcomes temptation, to stay within the threatened boundary of the rational, was a scenic and musical epiphany.

Next evening, the very day on which Russia tried to redraw the boundaries of Georgia (whose State Ballet appeared in the festival’s first week), there was Gergiev with an unashamedly nationalist Russian opera, Shchedrin’s adaptation of a Leskov novella, a 110-minute medley of folk tales in which three soloists took multiple roles. The lack of surtitles, not to mention an interval, left me feeling somewhat stupefied, as did the stylistic conglomerate of Shostakovich, balalaika music and the Carl Orff of the dreaded Carmina Burana.