Following are a number of back-translations of John 1:8:

• Uma: «Yohanes, it was not he who was that light. The reason he came was to spread that light to all people.» (Source: Uma Back Translation)
• Yakan: «Yahiya was not this light. But his mission/purpose for coming here was to tell about the light.» (Source: Yakan Back Translation)
• Western Bukidnon Manobo: «As for this John, he is not the one who is that light, but rather he is the one who explains who the light is.» (Source: Western Bukidnon Manobo Back Translation)
• Kankanaey: «Juan was not the light itself, but rather the one who came to confirm/verify concerning the light.» (Source: Kankanaey Back Translation)
• Tagbanwa: «It isn’t that he was the one who was the light. He was caused-to-be-a-person because he would be testifying about this light.» (Source: Tagbanwa Back Translation)
• Tenango Otomi: «John is not that one who opens the hearts of the people.» (Source: Tenango Otomi Back Translation)
• Ojitlán Chinantec: «John was not the one who illuminates people. He came to point out that one.»
• Yatzachi Zapotec: «It wasn’t John who brought light, but rather he came speaking about the person who brings light for mankind.» (Source for this and above: M. Larson / B. Moore in Notes on Translation February 1970, p. 1-125.)
• Hiligaynon: «Juan was not the light, but-rather he came/arrived to tell who is the light.» (Source: Hiligaynon Back Translation)
• Mairasi: «He himself was not that Light. But for the purpose of testifying about that Light he came.» (Source: Enggavoter 2004)
• Bariai: «He wasn’t that light, but he came to expound talk about that light.» (Source: Bariai Back Translation)
• Kupsabiny: «John came and told the people concerning/about that light, but that light was not him.» (Source: Kupsabiny Back Translation)

See also this devotion on YouVersion .