SENA Appendix C shows Manx Gaelic in the same language group as Oghamic Irish in "early period" (pre-1100), and compatible with English/Welsh. It also shows Manx Gaelic in the same language group as Middle Irish Gaelic and Early Modern Irish Gaelic in "late period" (1100-1600), also compatible with English/Welsh.
I'm sure this was already known, but just in case anyone was wondering.
"You asked for suggestions on bynames meaning 'healer' or
'redhaired' which would be appropriate for a medieval English
woman named <Sabyn>. Here is the information we have found."
translate it, and then use the search box on the left to hunt for names.
Provides documentation of two variants of Caerphilly from the 13th century - "Caerfily" and "Kaerfili".
The following citations are all from the Dictionary of the Place-Names of Wales by Owen & Morgan.
Bridgend: <Bryggen Eynde> 1444, <Brugeende> 1452, <Pennebont>, <Pont Newith on Ogor> 1536-9, <Brygend> 1542, <benn y bont> 1550-1600. The <Pen>/<Pont> forms are Welsh, the others are English. The town developed next to a bridge thought to have been built c. 1425.
Cardiff: <Kard'> c. 1102, <Kairdif> 1106, <Cardythe> 1555, <o gaer dydd> c. 1566. "The earlier form was <Caerdyf> in which <-tyf> is derived from the genitive singular of the original British word which gave the river name Taf."
Caerphilly: <Kaerfili> 1271, <Kaerphilly> 1314. The <caer> may be a reference to the small Roman fort which adjoined the castle.
Glamorgan: <morcanhuc> 1136-54, Morgannoc> 1191, <Glamorgan> 1315, <Glamorgan>, <Morganok> 1322, < Morgannok> 1403.
Swansea: <Swensi> c.1140, <Sweynesse> 1153-84, <Sueinesia> 1187, <Sweinesei> 1209-10, <Sweineshea> 1210, <Swense> 1235, <Swe(y)neseye> 1277, <Swannesey> 1505, <Swanzey> 1598-1600, <Swansea> 1530, <Abertawe> c.1191, <Abertwai> 1192, <Aber Tawy> c. 1300. The <aber> forms are, of course, the Welsh ones.
"Index of Names in Irish Annals: Masculine Descriptive Bynames"
"The place names of Stirlingshire"