[Talk-GB] The Welsh for "Brighton"

[Jbrsk B]

The way bounding Brighton (341820414) is tagged name:cy =Trellachar

Using Microsoft Translator I found that Tre=town and llachar=bright,
but I can find no other example of Trellachar on the internet. Has
Trellachar been invented by the very person who tagged it, and if so
would that be valid or useful?

According to wikipedia, "Brighton" (officially "Brighthelmstone" prior
to 1810) doesn't mean "Bright town" but probably "the homestead of
Beorthelm" or possibly "stony valley".

I'm just curious what people think about this!