You are getting that error because you are missing a line in your batch file which sets the Qt Plugin Path. The batch/ command file suggested in the link you posted does not contain that line.
The line in the batch file for my qgis installation looks like this:
However, your paths would be different as you say you used the standalone installer.
What I would suggest you do is to find the
python-qgis.bat file located in the bin folder of your qgis installation.
In your case, since you used the standalone installer, the batch file should be found in
C:\Program Files\QGIS 3.4\bin\python-qgis.bat
Open this batch file in a text editor and copy the line which begins with:
Edit your current batch file which you have created based on the instructions in Gary Sherman's blog by pasting in the line which sets the Qt Plugin Path and save.
However, without knowing what your batch file looks like, you may still have other problems. All the paths for your installation will be different to those in Gary's blog because you used the standalone installer. In the long run, you may find it easier to re-install QGIS with the OSGEO4W installer.
I have an OSGEO4W install and, using this batch script to start PyCharm:
start "PyCharm aware of QGIS" /B "C:\Program Files\JetBrains\PyCharm Community Edition 2017.2.3\bin\pycharm.exe"
I can run:
from qgis.core import *
qgs = QgsApplication(, False)
with no errors.