В базе R:
# Make sure your locale is English
Sys.getlocale() # can update with Sys.setlocale(LC_TIME = 'en_US.UTF-8')
# Remove "th", more generally the first sequence of lower-case letters
Date_String <- sub("[a-z]+", "", Date_String)
# Now specify the format for as.Date()
as.Date(Date_String, format = "%d %B %Y")
[1] "2020-01-19"