The Internet is an endless stream of useless information, whatever you want as long as it's utterly pointless it's bound to be on there.
Therefore, this morning when I suddenly found myself in need of a Welsh translation of "My hovercraft is full of eels" (as you do), I had absolutely no doubt that some sad lonely individual would have created a page with various obscure translations including Welsh, and hey presto
here's one.
Nice to know the internet is there for a purpose.