This gets all Finder tags labels.

You can also select only the custom tags (ignore the system ones):

func customTagLabels() -> [String] {
    let url = URL(fileURLWithPath: "\(NSHomeDirectory())/Library/SyncedPreferences/com.apple.finder.plist")
    let keyPath = "values.FinderTagDict.value.FinderTags"
    if let d = try? Data(contentsOf: url) {
        if let plist = try? PropertyListSerialization.propertyList(from: d, options: [], format: nil),
            let pdict = plist as? NSDictionary,
            let ftags = pdict.value(forKeyPath: keyPath) as? [[AnyHashable: Any]]
        {
            return ftags.flatMap { tag in
                if let n = tag["n"] as? String,
                    tag.values.count != 2
                {
                    return n
                }
                return nil
            }
        }
    }
    return []
}