The OpenStreetMap wiki contains lots of guidance and advice for anybody who wants to add to the map as a resource.
Anybody in the world can contribute Welsh-language names to OSM. We think there are important considerations to keep in mind.
Therefore here is an attempt to create a draft set of editing policies. They currently live on Google Drive. In the long term it may be possible to put them on the OpenStreetMap wiki if the wider community is willing. In the meantime you are warmly welcome to offer us feedback on them. Feel free to contact us or leave a comment on the doc itself.