Missionaries and the Written Language
The language was standardized in the 19th century. It was adopted by all the dialects to create some uniformity in Yoruba in spite of the differences. The 19th century was another effort to standardize the language. Initial efforts were first made in the 17th century by English missionaries and priests.
They developed a written language using the Ajami script. Vocabulary lists and grammar were developed and this helped later when Bishop Samuel Crowther used the Latin alphabet to translate a Yoruba-language Bible.