Fascinating Charlie Chan movie for a number of reasons. Filmed during the summer of 1939, a month before the official start of WW2 with the Poland invasion by German forces, the story is set in September of 1938, as Europeans are bracing for war over Hitler's Czechoslovakia territorial demands.
The film begins with a newsreel style rundown of the events leading up to that date, including archival footage. As part of the plot, there is mention of the evening light blackout (thus the title City In Darkness) laws, which many saw as government over-reach. The plot also involves all manner of corruption, and black market hi-jinks during a tense time leading up to war. Everything old is new again.
Yes, the film title (Treasure Island) on YouTube is incorrect, but the film in the link is definitely City In Darkness.