CKAN 2.9.2

Ubuntu 18.04

Describe the bug
The error occurs after upgrading from Python 2.7 to 3.6.
When navigating to a dataset the data isn't shown, but a loading spinner animation.
The devtools reveal there was an XHR call to /api/i18n/de which responded with a 500 error status code.
The web server logs contain an error message:
File "/usr/lib/ckan/default/lib/python3.6/site-packages/simplejson/decoder.py", line 404, in raw_decode return self.scan_once(s, idx=_w(s, idx).end()) simplejson.scanner.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

I think the cause is that the js files in /usr/lib/ckan/default/src/ckan/ckan/public/base/i18n are empty. First there was a file permission problem I had to solve. Then you could watch them being created one by one on the first run. The files in the old Python 2 environment are not empty. I tried to copy de.js from Python 2 to Python 3 environment, but this doesn't work and results in a different error:
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 156: ordinal not in range(128)

But how do I know if the XHR call is related to the dataset problem?

I guess there is some sort of unicode incompatibility between Python2 and Python3. To avoid unicode problems I replaced the german i18n file (de.js) in the new Python 3 env by the english file (en.js) from Python 2. After that the dataset is shown and the error 500 is gone.

Steps to reproduce

• Upgrade Python 2 to Python 3 (https://docs.ckan.org/en/2.9/maintaining/upgrading/upgrade-to-python3.html)
• Run application (sudo systemctl start apache2)
• Open page with dataset

Expected behavior

• dataset is being shown
• Status 200 for XHR request /api/i18n/de
• i18n js files not to be empty

Additional details
Stack trace:

2021-04-28 10:05:39,522 ERROR [ckan.config.middleware.flask_app] Expecting value: line 1 column 1 (char 0)
Traceback (most recent call last):
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/lib/ckan/default/src/ckan/ckan/config/middleware/../../views/api.py", line 482, in i18n_js_translations
    translations = json.load(open(source, u'r'))
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/simplejson/__init__.py", line 459, in load
    use_decimal=use_decimal, **kw)
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/simplejson/__init__.py", line 516, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/simplejson/decoder.py", line 374, in decode
    obj, end = self.raw_decode(s)
  File "/usr/lib/ckan/default/lib/python3.6/site-packages/simplejson/decoder.py", line 404, in raw_decode
    return self.scan_once(s, idx=_w(s, idx).end())
simplejson.scanner.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Screenshot: