There's a reason Donald Trump bangs on about China. Its emerging economy has dragged America's down and shifted capitalism's centre. It has opened up a new frontier; "the greatest pool of untapped consumers the world has ever known" - or so says the protagonist of Chinglish, Daniel Cavanaugh (Gyuri Sarossy), a smarmy Cleveland salesman out in China on business. Trump would like him. They're both into the art of the deal. Bigly.

Thing is, as Daniel discovers to his detriment, there are two sides to any deal and doing one in China takes all kinds of translation. He's flown to Guiyang province to secure a contract to supply signs for a new cultural centre, armed with evidence as to how easily - and how embarrassingly - English translations can go wrong. Without due care, disabled loos become 'Deformed Man's Toilets.' It cuts both ways though: English can mangle Mandarin in its own ways. Hence, Daniel's hiring of a local ex-pat consultant, Peter (Duncan Harte), to oil the cogs of his deal and translate across a linguistic and a cultural divide.

Only, as David Henry Hwang's play makes clear, nothing quite translates exactly – least of all capitalism itself. For all that China's economy looks to have embraced western principles, Daniel discovers that its free market is nothing of the sort. Instead of competition, he encounters corruption. Behind the façade of freedom, there's authoritarianism; behind trade deals, nationalism.

Nobody's quite what they seem here. Daniel's not the success story he makes out, but nor is Peter. Rather than a local expert, he's a teacher who holds sway over the culture minister (Lobo Chan), although not his deputy (Candy Ma, excellent), who strikes up a relationship – business as well as pleasure – with Daniel directly. In cutting out the middle-man, they come to an understanding of their own.

Chinglish plays out in a criss-cross of languages - English one way; Mandarin the other - and a lot of its drama comes from misinterpretation, be it translator's error or consultant's editing. Surtitles let us see the subtext and, for all that confusion and crossed wires can be ticklish, the prolonged mugging and miming that goes with it grows exhausting. Whole scenes resembles infuriating games of charades.

Hwang's plot has its contrivances – not least the sense, at the end, that everything's played out according to some mastermind's plan – but it's not helped by a production that plays it broad. So broad, in fact, that it teeters towards racial stereotypes of its own – though maybe that's a matter of translation too. Where Hwang gently ribs the oddity of unfamiliar etiquette – brusque mobile phone manners, for instance – Keates' cast send their characters and their customs up. There's more focus-pulling here than at a cameramans' convention, as disinterested waiters roll their eyes and unreliable translators huff, puff and try to bring the house down.

Even Sarossy, usually such an easy stage presence, goes into overdrive. He flags down Daniel's desperation with wild eyes and flared nostrils – the David Haig school of acting – rather than simply letting us glimpse the sweat patches beneath his blazer. As Peter, Harte does the same, upping his camp eccentricity that lets us get ahead of the play. We see these two for the down-and-outers they are from the get-go, both clearly trying to get themselves lost in translation and so start over.

Chinglish runs at the Park Theatre until 22 April.