Some tests, and some functionality, will not be enabled unless a full set of 32-bit character encodings are available through Python.
The feedvalidator relies on html5lib for parsing HTML.
The package 'iconvcodec' provides the necessary codecs, if your underlying operating system supports them. Its web page is at http://cjkpython.i18n.org/#iconvcodec, and a range of packages are provided.
Python 2.3.x is required, for its Unicode support.
To run with Docker: docker build -t feedvalidator . docker run -p 8080:80 feedvalidator