I'm slogging through the character names index and a Welsh pronunciation guide (very necessary — sorry to do it to you folks. One of my beta readers is complaining bitterly. I say, could be worse – could be a Russian novel.) This requires me to look up every name and make sure I provide some clue about how to say it. Welsh looks much harder than it is because of unusual spelling conventions. “Gruffydd” is Griffith, “Rhys” is Reece, “Vachan” became Vaughan, and so forth, but there are some genuine problems, too.
To begin with, the name of one of my main characters turns out to be the wrong gender. (No, I'm not telling you which one.) That's fixed now (that is, I fixed the name, not him.) Too bad, I liked that name.
Secondly, you can't just look up Welsh words in a dictionary. Perhaps you didn't know this… Celtic languages share a phenomenon known as “mutation” and are annoying enough to change the spelling accordingly. This means, when you pronounce a word differently because of the influence of its surrounding words or grammatical syntax, you spell it that way.
We're used to this in English for vowels in some of our older words, such as our class of strong verbs. We share with other Germanic languages couplets like “run/ran”, “fall/fell”, “know/knew”. Initial letters, on the other hand, rarely do this in English, so it doesn't seem so bad because we only have a few of them, and the initial letter isn't involved. It's different in Welsh.