rua torta lua morta tua porta.
Basil Hatim and Ian Mason in Discourse and the Translator wrote “In this short poem, phonemic form is everything, the words themselves are evocative: a small town with ‘winding streets’ (rua torta), a ‘fading moon’ (lua morta) and the hint of an amorous affair: ‘your door’ (tua porta). But their impact is achieved almost solely through the close rhyme and rhythm; the meaning is raised from the level of the banal by dint of exploiting features which are indissociable from the Portuguese language as a code.
Valentín García Yebra, spanish philologist and translator, in his 1983 book En Torno a la Traducción relates that he gave up the attempt to translate the poem even into Spanish, a language which shares certain phonological features with Portuguese.
Cassiano Ricardo wrote “Serenata sintética” in 1957. Simple yet untranslatable.