This one drove me up the wall. The days and months in the datePicker() kept coming back as Chinese. Turns out the issue stemmed from a new theme, Experon Pro. This is probably not the best way to fix this issue, but it’s fixed and allowing me to move on to new tasks.
In lines 41 and 42, and your language of choice.
If you know a better way, please share as I would enjoy learning more on how WordPress functions.