Here are a few quick tips to remember when pronouncing Celtic vowels. They are "pure" sounds similar to Italian and Spanish.

a ("ah")
e ("ay" or "eh")
i ("ee")
o ("oh")
The letters w ("oo"), y ("ee", "i", or "eh")
u (pronouced with a deeper "ee")

The Welsh language has five consonants not normally occuring in the English language. They are:
ch (a gutteral sound like the German ch),
dd ("th" like the word "then")
ff (like the English sound of "f")
rh (a breathy rolled "r")
ll (a cross between "l" and "s")

A single f in Welsh is pronounce like a "v".
All "r's" are rolled.

When pronouncing multisyllabic words the emphasis falls on the next to last syllable. For example:
dyffryn is pronounced "DUH-frin"
capel is pronounced "CAH-pel"
Eglwys is pronounced "AYG-looees" making sure that the "oo" and "ee" sound like one smooth syllable.

Many of the Welsh immigrants who settled in Gallia county came from Mynydd Bach. This is pronounced "MUHN-ithe BACH" with the ch formed well in the back of the throat. Come on, try it...

Another Welsh word to learn is Llangeitho pronounced "Llahn_GAY-thoh".

Two Welsh American publications found in your research will make reference to Y Cyfaill which is pronounce "uh CUH-vayll" and Y Cenhadwr, pronounced "uh ken-HAHD-oor."

Common meanings of Welsh Place-Names