Some attempts have been accomplished in the past in transcribing the Saho language, starting from the non-scientific transcription of Henry Salt (1814)¹, Antoine d’Abbadie (1843) and Heinrich Ewald (1844) till the Lepsius’² method followed by Leo Reinisch in his publications on Saho (from 1877 onwards).
Carlo Conti Rossini (1913) used what is known as “Italian transcription”³.
It was the linguist and missionary Francis E. Mahaffy that developed, at the beginning of the sixties of the XX century, a personal system of latin transcription for the Saho, using special signs for the retroflex [ɖ], the ejectives [tʼ] and [sʼ], the pharyngeals [ħ] and [ʕ] and other few sounds, as well as for the long vowels.
Around the 1985 was developed in Eritrea what is now the official latin orthography of Eritrean Saho.
Recently, also in Ethiopia was developed an official system for writing the Saho language in the Irob province of the Tigray region, but using the fidel orthography.
See here for the system used by Mahaffy for some signs, compared with the Eritrean and Ethiopian ones.
See here for a comparison table between the Eritrean Saho and the Ethiopian Saho orthographies (with Abyssinica SIL font key [ABSk], International Phonetic Alphabet [IPA] and the transcription used by the Encyclopaedia Aethiopica [EAE]).
¹For the complete references see Bibliography.
²See C.R. Lepsius (1863) Standard Alphabet for Reducing Unwritten Languages and Foreign Graphic Systems. London: Williams&Norgate. Available online at https://archive.org/details/standardalphabe04lepsgoog.
³For an exhaustive article on the transcription for the languages used in Ethiopia and Eritrea, see Rainer Voigt (2014) “Transcription system”. In Alessandro Bausi (in cooperation with Siegbert Uhlig) (eds.) Encyclopaedia Aethiopica, Vol. V: 533b-337b. Wiesbaden: Harrassowitz Verlag.