This research aims to describe the importance of diplomatic language and to confirm its effectiveness in international discourses as its form and content are very distinct from other types of languages used in trade, culture, literature, sports, etc. The Prophet (PBUH) paid attention to this diplomatic language to spread the call of Islam and to convey the message of faith to the kings and princes in Arabic or in its translation in other languages at the end of the sixth year of Hijrah. The research adopted descriptive analysis method to analyze selected texts from a number of al-hadiths concerning the functions of the diplomatic actions carried out by his companion. This study concluded that this diplomatic language indeed needs translation as it had played an important role in the success of the mission of international discourses. It helped to bring the meaning of the messages to the understanding of the kings and princes and it also aided to deliver the elements of propagation into their minds and souls. In return it led to their recognition of the truth of the propagation and their acceptance of the call carried out by the lines of these propagation letters. Keywords: translation, discourse analysis, diplomatic language, international relations, Muhammad’s letters