"Did you go to the bank?"
Translation:Est ti i'r banc?
Would you not be able to say either 'Rwyt ti wedi mynd i'r banc' or 'Dych chi wedi mynd i'r banc'?
Wedi is the perfect tense which talks about the immediate past.
Dych chi wedi mynd i'r banc? or Wyt ti wedi mynd i'r banc? means 'Have you gone to the bank?
This is a different meaning to Did you go to the bank especially in Welsh.
Est ti ti'r banc = literally Went you to the bank