"I will feel that the Dedjatch has robbed me to the tune of 866"
I fail to find the meaning of the word in the dictionaries, help me understand it, please? Is it some local term?
In Amharic, the primary language in Ethiopia (or Abyssinia at the time of Rimbaud's writing), Dejazmatch or ጽጅዝምች (sometimes Dejatch) means literally
or more in terms of functioning role, translated as
The spelling 'Dedjatch' is presumably a francophone spelling ('dj' is how the French spell the rare in French voiced palatal affricate which is 'j' in English).
Searching for 'dejatch' yields many sources saying "Prince (Dedatch) Alemayehu" or just "Prince Alemayehu", and the interpretation that 'Dejatch' is a title of nobility works in all the contexts it is mentioned in those texts.
The usual term for 'prince' in Amharic is ልዑል= liuli, the son of the emperor. But translation and cultural choices can be arbitrary and the English (and French and Italian) somehow settled on 'prince' in this situation.
The list of titles of nobility in Abyssinia gives the real correspondence.