"Dych chi'n mynd i Aberteifi?"
Translation:Are you going to Cardigan?
Although the Welsh and English versions of place names are often the same or very similar - usually from the Welsh e.g. Llanelli but sometimes from the English e.g. Shotton, when a place name is very different in both languages, it's interesting to trace the different meanings.
Here, we have Aberteifi in Welsh i.e. aber "mouth" of the river Teifi whereas in English, Cardigan is an anglicisation of Ceredigion "Ceredig's land".
One of my favourite examples of differing names is Abertawe vs Swansea. Abertawe means the aber "mouth" of the river Tawe and shows the perspective of the natives - the Welsh - looking out from the land they lived on towards the sea. Swansea on the other hand is from the Viking language Old Norse Sveinsey i.e. "Sveinn's island". Swansea was a Viking trading post and shows the perspective of outsiders who sailed across the sea looking towards to the land.
Some places in Wales have a separate Welsh and English names. In this case, Aberteifi means "the mouth of the River Teifi" whereas English Cardigan is an anglicisation of Welsh Ceredigion meaning "Ceredig's land". Both names have grown up and been used for centuries by Welsh and English speakers separately, meaning nowadays Aberteifi is what we use when we're talking Welsh, Cardigan when we're talking English. In other cases, there's just one name used by both languages, for example Llanelli is the same in Welsh and English. When you learn place names in Welsh, you have to check whether there are separate Welsh and English forms or whether they both use the same one.
Because Cardigan is the name of the town in English. Nobody says "I'm going to Aberteifi". That's no more correct than saying "I'm going to München", or "I'm going to Ciudad de México." If you say that in English, people will just look at you blankly, or think you're showing off.
Most towns in Wales have a Welsh name and an English name; sometimes, they're very similar, like Cardiff (EN) / Caerdydd (CY), Barry (EN) / Y Barri (CY), Barmouth (EN) / Bermo (CY), but often they're completely different such that you wouldn't even think they were connected: Holyhead (EN) / Caergybi (CY), Monmouth (EN) / Trefynwy (CY), Brecon (EN) / Aberhonddu (CY) etc...
Some towns, especially in more rural parts of Mid Wales and North Wales, have a Welsh name but no English name (e.g. Aberystwyth, Machynlleth, Betws-y-Coed), but generally these are in the minority.
We do NOT translate proper nouns!
Nonsense, when we're talking about names of countries and of famous cities.
In English, the capital of Italy is Rome and the capital of Thailand is Bangkok. We don't say that the capital of Italia is Roma or that the capital of Prathet Thai is Krung Thep Maha Nakhon.
Similarly, we don't say that the capital of Cymru is Caerdydd; we say that the capital of Wales is Cardiff.
And the other way around, in Welsh we do not say that London ydy prifddinas England but instead that Llundain ydy prifddinas Lloegr.