This study pioneers in applying the relevance theoretical framework developed by Gutt (1991, 2000a) and based on Sperber and Wilson's relevance theory (1986, 1995) to Chinese xiehouyu translations. A Chinese xiehouyu is an idiom or an enigmatic folk saying consisting of two parts. This study examines direct approaches and indirect approaches with or without the substitution of appropriate metaphors. It argues that while relevance theory is effective in both approaches, it is particularly important for indirect translation because there are various ways of translating a xiehouyu indirectly, depending upon what meaning aspects of the original the target audience will find relevant. A match-up metaphor in the target language may not always be available, but whenever possible the strategy of substituting metaphors should be utilised to maximise contextual effects and minimise the processing effort; this is probably the most effective way to achieve optimal relevance. As an instance of interpretive use, a translation's success depends on the achievement of optimal relevance. The translator has to pay attention to the kind and degree of interpretative resemblance the audience expects: that is to say, a translator should take the target audience's cognitive environment into account and choose the most applicable approach to guide the audience in achieving optimal relevance.