HK Cinema - 1963
It may not strike anyone as a milestone, but for those of us HK film fans who speak no Chinese this 1963 ruling had a huge impact. The British perhaps concerned about anti-colonial or leftist propaganda made it mandatory for all films produced (and perhaps shown) in HK to have English sub-titles.

With the handover of HK back to China in 1997, many people were concerned that this regulation would come to an end and our HK viewing days would be over. So far it has not happened - perhaps out of a sense of tradition or perhaps economically it is a positive thing to make these films as internationally accessible as possible.