One problem is the commoner vowels. In most languages, a, e, i, o, u is ah, ay, ee, oh and oo (ignoring those calling for umlauts, etc.) while English usually calls for ay, ee, ai (aye), oh and yew.
Among the consonants, c gives trouble because it may be hard (k) or soft (see). In Italian, ce is che, ci is cha, ch is k, and co, cu, ca etc. are k. Irish words transcribed into English, e. g., Sean, Siobhan (Sioban) must have similar rules, but we have no handy reference unless some Irish individual tells us- otherwise we apply the English rules. It would be nice to know the general guidelines.
Ciaran would be a complete mystery to most over here. At a guess- Karen? Sharon?