There isn't a direct translation of the name "Fred" in Gaelic (either Scottish Gaelic or Irish Gaelic) that's a common or traditional equivalent. Gaelic names tend to have meanings and are often chosen based on those meanings. To find a Gaelic equivalent, you'd need to consider what aspect of "Fred" you want to reflect.
For example, if "Fred" is short for "Frederick," you could look at Gaelic names with similar meanings related to peace or ruler. However, there isn't a single perfect substitution.