add multiple langue using Astrotomic / laravel-translatable package and laravel - laravel

Question

i am new in laravel and use Astrotomic / laravel-translatable package for translation
i have problem when i want to add two langue at same time.
i have name_en,name_ar,discription_an,disriptionar as inputs fields.
i get this error Creating default object from empty value
so how can I solve my problem
this is link of package https://github.com/Astrotomic/laravel-translatable
// start add data
public function store(CategoryRequest $request)
{
// prepare data
$validatedData = array(
'url' => $request->url,
'slug' => $request->slug,
'status' => $request->status,
'last_updated_by' => auth('admin')->user()->id,
'created_by' => auth('admin')->user()->id,
'created' => time(),
);
$translated = array(
'name_en' => $request->name_en,
'name_ar' => $request->name_ar,
'description_en' => $request->description_en,
'description_ar' => $request->description_ar,
);
//start define categoru is sub or main
$request ->sub ==1 ? $validatedData['parent_id'] = $request ->category_id: $validatedData['parent_id']=null;
// start update data
DB::beginTransaction();
$add = Category::create($validatedData);
$id = $add->id;
// strat update category report
$categoryReport = CategoryReport::create(
['status' =>$validatedData['status'],
'category_id' =>$id,
'created_by' =>$validatedData['created_by']
,'last_updated_by' =>$validatedData['last_updated_by']]);
$add->translate('ar')->name = $translated['name_ar'];
$add->translate('en')->name = $translated['name_en'];
$add->translate('ar')->description = $translated['description_ar'];
$add->translate('en')->description =$translated['description_en'];
$add ->save();
DB::commit();
return redirect()->back()->with('success','تم اضافه البيانات بنجاح');
}