I am having the same issue when I use the OBS add "Video Capture Device" feature. I have a Blackmagic Ultrastudio mini recorder (which works and is it's own separate option under the "+" in the sources box) but when I try to add a different video capture device (a USB 3.0 DigitNow from amazon connected to a Sony RX100 iii) OBS crashes once I get to the screen to select either my webcam or the usb device. I get the option to reopen but then I am told "Failed to find locale/en-US.ini"
I get this crash/error anytime I try to use "video capture device" regardless if i chose my integrated webcam or an external device.
I'm running macOS Catalina on a MBP 2018, 15in, 2.6 I7 6 core processor with 2400 16GB DDR4.