Japanese Controlled Language Rules to Improve Machine Translatability of Municipal Documents

We report on experiments to test the effectiveness of controlled language (CL) rules on texts from Japanese municipal websites. We compiled a set of rules by trial and error, systematically rewriting Japanese source texts and analysing the machine translation (MT) outputs. We then employed native English speakers with little knowledge of Japanese as human evaluators and tested the understandability and accuracy of the English machine translated text. Comparing the results of four MT systems showed that the effectiveness of CL rules varies depending on the particular MT systems. A preliminary selection of optimal rules for each system showed more than 15% increase in MT performance. We also assessed the readability of the Japanese source texts and discuss the way to make them compatible with the quality of the MT outputs.