Translation Editor: Server Error. 415 Unsupported Media Type

[ceelian]

Whenever I try to set or change a translation in the translation web editor. Saving the translation fails with the following error. Translation with PO files works.

The JS Code of wagtail-localize tries to make a PUT ajax call to /cms/localize/translate/3/strings/9/edit/
with this form data:

------WebKitFormBoundary6jt1TZCYSnyBx8ta
Content-Disposition: form-data; name="value"

bar
------WebKitFormBoundary6jt1TZCYSnyBx8ta--

The return code is 415 Unsupported Media Type

Django Server only logs:

WARNING 2021-03-18 14:46:20,254 | 26 140661536054048 | log.py:224 | Unsupported Media Type: /cms/localize/translate/3/strings/9/edit/

Versions:
django==3.1.2
wagtail==2.12.3
wagtail-localize==0.9.5

[ceelian]

I just tried it again with the 1.0 RC3, still the same bug. @kaedroho have you any idea what might cause this error?

django==3.1.2
wagtail==2.14.1
wagtail-localize==1.0rc3

Thanks a lot.

[zerolab]

Does this happen with v1.0? I tried replicating the issue on a variety of browsers and could not.

One thing I suspect may be happening is the server receives an incorrect content-type header