"May I pay, please?"

Translation: Ga i dalu, os gwelwch chi'n dda?

[jonesrachael96]

Why does "talu" become "dalu" here?

[ibisc]

Because talu is the direct object of the conjugated verb ga(f), and so undergoes soft mutation. For example:

• Prynais i gar newydd - I bought a new car (car -> gar, direct object of prynais)
• Gaf i beint o chwerw? - May I have a pint of bitter? (peint -> beint)
• Bwytiff Siân bysgod a sglodion - Siân will eat some fish and chips (pysgod -> bysgod)
• Fe wnaeth Siôn dalu ei drethi y llynedd - Siôn paid his taxes last year (talu -> dalu)

[EllisVaughan]

It's because it is coming after a pronoun.