Save the following code snippet as local plugin (step 1):
local now = DateTime.now()
now:FormatLocalTime("LL", "en-150")
Restart studio (step 2), and open any place (step 3). You should get a following error:
Error in loading DateTimeLocaleConfig file of en-150 (Unable to load rbxasset://configs/DateTimeLocaleConfigs/en-150.json)
If you don’t get the error, try to repeat the last 2 steps (2,3) few more times.