Solved

This error happened when I follow the instruction in here. I set Unit file. I understood that LAN env valuable doens't transfer properly and it used default ascii. You can fix this problem with adding one line in unit file. It was a really long journey to find out....

[service]
Environment="LANG=en_US.UTF-8"

I didn't have any problem when I set my environment with mod_wsgi and Apache2. I just had to add "export LANG='en_US.UTF-8' export LC_ALL='en_US.UTF-8'" in /etc/apache2/envars path to upload file with non-ASCII filename.

This time, I set my env with Nginx and Gunicorn. But It occurs UnicodeEncoderError in every part where shows non-ASCII characters.

'ascii' codec can't encode characters in position 57-59: ordinal not in range(128)

I don't understand why 'ascii' codec is used to encode in Python3 and Django environment.

I searched and searched and searched. I checked and tried like below.

PostgreSQL check : Encoding UTF8
Django default encoding : utf-8
Ubuntu locale check : en_US.UTF-8 (I also tried 'ko_KR.UTF-8', because it has an error with Korean)
checked python 3 sys.getdefaultencoding, sys.stdout.encoding, sys.stdin.encoding : utf-8
adding charset utf-8; in /etc/nginx/sites-available/myproject
checked if Gunicorn call python2 instead of python3 : installing gunicorn with pip3 virtualenv and checked '#!/home/username/venv/bin/python3' in gunicorn file.
write import sys reload(sys) sys.setdefaultencoding('utf-8') in views.py : I understood it can apply to python2 and it is not recommended way.

I was suspicous that Gunicorn call python2 instead of python3 because python2 is also installed in my Ubuntu. If I check python -c 'import sys; print(sys.getdefaultencoding());', I can see 'ascii'. Python 2 has str and unicode. I concluded that Gunicorn doesn't have problem with it at the end.

I am still suspicious of python 2.7 which was preinstalled in Ubuntu16.04. Can you explain that What i am missing or misunderstanding?? I understood that ascii codec encode error could happen with Python2, not Python3.

Env Python 3.5 Django 1.11.1 Gunicorn 19.7.1 Nginx 1.10.3 Ubuntu 16.04 LTS