How do you say Russell in Gaelic?

There isn't a direct translation of the name "Russell" in Gaelic (either Scottish Gaelic or Irish Gaelic) because it's of Norman French origin. Gaelic names typically have meanings related to nature, attributes, or places. To use a Gaelic name that has a similar meaning or sound, you'd need to choose one based on the intended meaning of Russell (which itself has several possible etymologies). There's no single "correct" Gaelic equivalent.