1. A speech translation system including a control device, two or more speech recognition apparatuses, two or more translation apparatuses, and two or more speech synthesis apparatuses, wherein the control device comprises: a speech receiving unit that receives speech information from a first terminal apparatus that accepts speech of a first user; a speech recognition requesting unit that sends the speech information to each of the two or more speech recognition apparatuses; a speech recognition processing result receiving unit that receives, in response to sending of the speech information, two or more speech recognition processing results each including a speech recognition result for the speech information and a speech recognition score that indicates a probability of speech recognition processing from the two or more speech recognition apparatuses; a speech recognition result selection unit that selects a speech recognition result that is most probable by using the speech recognition scores included in the two or more speech recognition processing results; a translation requesting unit that sends the speech recognition result selected by the speech recognition result selection unit to each of the two or more translation apparatuses; a translation processing result receiving unit that receives, in response to sending of the speech recognition result, a translation processing result including a result of translation performed on the speech recognition result into a target language and a translation score that indicates a probability of translation processing from each of the two or more translation apparatuses; a translation result selection unit that selects a translation result that is most probable by using the translation scores included in two or more translation processing results received by the translation processing result receiving unit; a speech synthesis requesting unit that sends the translation result selected by the translation result selection unit to each of the two or more speech synthesis apparatuses; a speech synthesis processing result receiving unit that receives, in response to sending of the translation result, a speech synthesis processing result including a speech synthesis result for the translation result and a speech synthesis score that indicates a probability of speech synthesis processing from each of the two or more speech synthesis apparatuses; a speech synthesis result selection unit that selects a speech synthesis result that is most probable by using the speech synthesis scores included in two or more speech synthesis processing results received by the speech synthesis processing result receiving unit; and a speech synthesis result sending unit that sends the speech synthesis result selected by the speech synthesis result selection unit to a second terminal apparatus used by a second user, each speech recognition apparatus comprises: a speech recognition target speech receiving unit that receives speech information from the control device; a speech recognition unit that performs speech recognition processing on the speech information and acquires a speech recognition processing result including a speech recognition result and a speech recognition score that indicates a probability of speech recognition processing; and a speech recognition processing result sending unit that sends the speech recognition processing result to the control device, each translation apparatus comprises: a speech recognition result receiving unit that receives a speech recognition result from the control device; a translation unit that performs translation on the speech recognition result received by the speech recognition result receiving unit into a target language, and acquires a translation processing result including a translation result and a translation score that indicates a probability of translation processing; and a translation processing result sending unit that sends the translation processing result acquired by the translation unit to the control device, each speech synthesis apparatus comprises: a translation result receiving unit that receives the translation result from the control device; a speech synthesis unit that performs speech synthesis processing on the translation result, and acquires a speech synthesis processing result including a speech synthesis result and a speech synthesis score that indicates a probability of speech synthesis processing; and a speech synthesis processing result sending unit that sends the speech synthesis processing result to the control device.