There isn't a direct translation for the word "negro" in Gaelic (either Scottish Gaelic or Irish Gaelic) because the word carries a complex and offensive history. Gaelic, like many other languages, didn't have a word specifically for racial categorization in the way that "negro" was used. To refer to a person of African descent, you would use descriptive terms relating to their origin or appearance, similar to how you might describe someone's nationality or skin tone in English. For example, you might use phrases describing someone's skin color or their country of origin.
It's crucial to avoid using any term that could be considered racially charged or offensive. Focus instead on respectful and neutral descriptions.