I have released emacs-jinja2-mode-ng0 version 0.2.1 today. This release continues the development the original author made.
Version 0.2.1 mainly includes merges of open Pull Requests on github. In practice this just means there's now support for files with the '.j2' extension.
You can obtain the tarball release via the link above, or if you are using guix you can simply add my packages repository to your
GUIX_PACKAGES_PATH, which includes a definition for this emacs package.