This will be of particular interest if you want to provision your own server which produces map tiles in the Welsh language (or perhaps a different language of your preference). All code is licensed under GPL, allowing you to run it for any purpose, modify it, and redistribute it.
Please note that a basic knowledge of how to use the Linux command line is assumed.
The main tool is a Lua script called cartonamecy2name.lua which is run when importing data. It determines the name to be stored in the database, for any given entity on the map. OSM data is the main source for Mapio Cymru, particularly the name:cy and name tags, and also Wikidata name information via OSM’s wikidata tag. In editing these sources we also refer to open data from the Welsh Language Commissioner.
Many more details are given in the README file in the repository, including step-by-step instructions for use.
If you just want to use a Welsh-language map which already exists, ignore the above and head to openstreetmap.cymru!