What the guardian project does is great, but using markdown may lead to major headaches because of the lack of standards.
The Fedora project uses asciidoc (this was decided years ago and isn't related to i18n). And automation with po4a+weblate for a 1500 pages counting 1800000 words for a single publication system (antora) was challenging.
Using a less standardized format for more publication systems just make it way harder. Good luck!
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