Language:
كتاب الأحكام
93  
Judgments (Ahkaam)
(40)
Chapter: The translators of a ruler
(40)
باب تَرْجَمَةِ الْحُكَّامِ، وَهَلْ يَجُوزُ تُرْجُمَانٌ وَاحِدٌ
Sahih al-Bukhari 7195
Kharija bin Zaid bin Thabit said that Zaid bin Thabit said, "The Prophet (ﷺ) ordered me to learn the writing of the Jews. I even wrote letters for the Prophet (ﷺ) (to the Jews) and also read their letters when they wrote to him."

And 'Umar said in the presence of 'Ali, 'Abdur-Rahman, and 'Uthman, "What is this woman saying?" (the woman was non-Arab) 'Abdur-Rahman bin Hatib said:

"She is informing you about her companion who has committed illegal sexual intercourse with her."

Abu Jamra said, "I was an interpreter between Ibn 'Abbas and the people." Some people said, "A ruler should have two interpreters."

وَقَالَ خَارِجَةُ بْنُ زَيْدِ بْنِ ثَابِتٍ عَنْ زَيْدِ بْنِ ثَابِتٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم أَمَرَهُ أَنْ يَتَعَلَّمَ كِتَابَ الْيَهُودِ، حَتَّى كَتَبْتُ لِلنَّبِيِّ صلى الله عليه وسلم كُتُبَهُ، وَأَقْرَأْتُهُ كُتُبَهُمْ إِذَا كَتَبُوا إِلَيْهِ، وَقَالَ عُمَرُ وَعِنْدَهُ عَلِيٌّ وَعَبْدُ الرَّحْمَنِ وَعُثْمَانُ مَاذَا تَقُولُ هَذِهِ قَالَ عَبْدُ الرَّحْمَنِ بْنُ حَاطِبٍ فَقُلْتُ تُخْبِرُكَ بِصَاحِبِهِمَا الَّذِي صَنَعَ بِهِمَا‏.‏ وَقَالَ أَبُو جَمْرَةَ كُنْتُ أُتَرْجِمُ بَيْنَ ابْنِ عَبَّاسٍ وَبَيْنَ النَّاسِ‏.‏ وَقَالَ بَعْضُ النَّاسِ لاَ بُدَّ لِلْحَاكِمِ مِنْ مُتَرْجِمَيْنِ‏.‏
Reference : Sahih al-Bukhari 7195
In-book reference : Book 93, Hadith 56
USC-MSA web (English) reference : Vol. 1, Book 89, Hadith 303
  (deprecated numbering scheme)