It is very difficult to translate from one language to another and maintain continuity of thought, let alone preserving rhyme and rhythm.When translating a book, a literal translation is feasible.  This is impossible with music or poetry, since one must maintain rhyme.Sometimes bacause the task is so daunting,  the interpretor takes a general feeling of the song, and writes entirely different lyrics. When I have found different sets of lyrics, I have included them.  No one set is correct - it is a matter of choice and what sounds best to the reader.  -Bob Penry-

The question also arises, "Why do Welsh hymns have titles that have nothing to do with the lyrics?"  Different congregations often have different lyrics for the same tune, or the same lyrics are sung to different tunes.  In years past, organists were hired, and would travel from church to church.  While lyrics change, tunes do not.  Therefore each melody was given a tune name.  This was often the name of a locality, perhaps where the author lived. (For instance, Cwm Rhondda means the Rhondda Valley.)  The organist then recognized the song, regardless of the lyrics.  Some hymnals still maintain the tune names, either in parenthesis below the title, in the composer area, or in an appendix to the hymnal.