Victor Swanson was born in Gonarum, Blekinge, Sweden in about 1880, and his wife Anna Belle (née Marshall) was born December 28, 1877 in White Pigeon, St Joseph, Michigan, in the United States. He was a translator of colloquial Arabic (Moroccan and Mogrebi dialect New Testaments) and Berber (book of Luke in Tamazight, Central Atlas and Shilha Berberi). Victor came from Sweden to the United States at the age of twelve, and was never naturalized, so he continued to be a Swedish citizen throughout his life.
When he and his wife first went to Morocco, they went without passports and lived in the primitive conditions of Morocco at that time. They married in Morocco. They worked first with Gospel Missionary Union and later with North Africa Mission (based in London).
For the few Moslems who became Christians, the Swansons encouraged them not to give up their way of living, or become “Europeanized.” Anna Belle was a talented musician, but only had access to a “folding organ” because it was portable.
They stayed in Morocco until 1941 or 1946 (a total of 35 to 40 years according to different sources).  Their children are John Marshall and Grace Caroline.  Victor Swanson must have died sometime after 1967, after he finished translating the Mogrebi Arabic New Testament. 
According to Anna Belle news article from 1941, they had been there 35 years. https://www.newspapers.com/clip/31546166/ (read this for more information!). So because their daughter Grace said her parents had been in Morocco for 40 yrs, they would have been there until about 1946: https://www.newspapers.com/clip/31546479/