Synthesized voice is widely used in a human-computer system to provide recommendations for decision makers. In order to compare the influence of the synthesized voice and the natural voice as well as the explicit and implicit communication styles on decision makers of different nationalities, a decision making experiment is conducted with 24 Chinese students and 24 German students. The acceptance of recommendations, the change of confidence level, the perceived influence, the extent of trust in the recommendation provider, the satisfaction degree, and the future collaboration intention with the project are identified in the experiment. The statistical results show that compared with the natural voice, the synthesized voice significantly increases the decision maker's confidence level, but the decision makers perceive lower influence and have less future collaboration intention under the synthesized voice. Overally, the decision makers accept explicit recommendations more often than implicit recommendations and have more positive evaluations on explicit advisors than implicit advisors. For explicit recommendations, German decision makers perceive more influence than Chinese decision makers; for implicit recommendations, Chinese decision makers accept recommendations more often than German decision makers. Based on the results, the recommendations for the synthesized voice software design are made.