OK, I see the issue now. For the contributing, guide and reference articles there is a single markdown file (README.md) to be translated.
However, for the tutorial articles there are two markdown files: README.md and before-1st-h2.md. The tutorial README.md files are autogenerated from the welcome-to-xod project using generate-tutorial-docs.js. I think the before-1st-h2.md file is manually created for the Fritzing scheme, but I may be wrong. I agree that for the tutorials there doesn’t seem to be guidance on how to do the translations.
As you are probably aware, XOD is in a state of flux (see That’s all. XOD is looking for for a new owner), so it may take some time to get instructions on how to translate the tutorials. Also, I’m not sure how long it will take for your translated articles to go live. If despite these uncertainties you would still like to contribute, you could start by translating the guide and reference articles.