Got to be honest; I don't know that these chords are right, but they sound righter to me than some
other versions I've found... Barr chords sound best on this, I think. Also, I've attempted to include
a translation of the Welsh lyrics in square brackets [thanks Google!]

       D              F#m
Well isn't it a lovely day
      G                   A
Oh, I'm feeling all brand new
        D             F#m
Well isn't it a lovely day
      G                  A
Oh, boating on sunday with you
         G               A
And if you really want to kiss her
     G            A
Just go right up and tell her
      D               G   A   D      A
Oh, isn't it a lovely day for love
         D              F#m
Well isn't it a lovely day
        G           A
Oh, my patio's on fire
        D               F#m
Well isn't it a lovely day?
        G                 A
Oh no, words are wisdom from liars
          G             A
And if you really want to kiss her
          G           A
Just go right up and tell her
          D           G    A
Oh, isn't it a lovely day for
    D      G
Mae'n bwrw glaw
[It's raining]
D        G
So dal fy llaw
[So hold my hand]
            G              A
Ond mae'r gaeaf mor hir
[But the winter is so long]
               G           A 
Mae'n cymryd gormod or tir
[It takes over too much of the land]
D        G
Dal fy llaw
[Hold my hand]
    D      G
Mae'n bwrw glaw
[It's raining]
          G      A
Ond mae'r gaeaf mor hir
[But the winter is so long]
             G         A
Mae'n cymryd gormod or tir
[It takes over too much of the land]

(Repeat chords to end)