Possible Clues:

• Language in which 'dd' and 'ff' are treated as single letters of the alphabet
• Like rarebit
• From Gwynedd, say
• Englishwoman ignores moaning from family living in Cardiff
• Anthony Hopkins, by birth
• Language starts to worry English ladies staying here
• Cymraeg, in English
• Language that gave us ''corgi''
• & 2 Down Cheese on toast
• Language in which 'Thank you very much' is 'Diolch yn fawr iawn'