What is the oldest written source in this country that mentions this right?
Indonesia
The 1964 Provisional Constitution of the Republic of Indonesia guaranteed freedom of expression to all in Article 19.
References:
R.; Jones Supomo, Garth N., Translator. Provisional Constitution of the Republic of Indonesia (1964) https://heinonline.org/HOL/Page?collection=cow&handle=hein.cow/proconindo0001&id=29&men_tab=srchresults