"A allaf fi fenthyg dy reolwr, os gwelwch yn dda?"
Here's a breakdown of the phrase:
* A allaf fi - "May I"
* benthyg - "borrow"
* dy reolwr - "your ruler" (literally "your ruler")
* os gwelwch yn dda - "please"
You can also say:
* "Gallaf fi fenthyg dy reolwr, os gwelwch yn dda?" - "Can I borrow your ruler, please?"
* "A gaf i fenthyg dy reolwr?" - "Can I borrow your ruler?" (more informal)
It's important to use a polite tone when asking for something in Welsh, as in any language.