Here’s a link to that thread on the old forum. It was almost two years ago!
http://www.saysomethingin.com/welsh/viewtopic.php?f=6&t=7499&start=0
There’s also another (older) thread there, started by someone in an American theatre company that was doing Henry VI and wanted to have appropriate Welsh (where the script just says “speaking Welsh”). http://www.saysomethingin.com/welsh/viewtopic.php?f=5&t=4688&start=0