Write on $_POST an array inside DB like result - php

Question

I have a problem on $weight_class_title.
When the data is saved it wrote in the database array.
Tk.
the result of var_dump($sql_data_array);
array (size=4)
'weight_class_title' =>
array (size=1)
'weight_class_title' => string 'tt' (length=2)
'weight_class_key' => string 'pound' (length=5)
'weight_class_id' => int 5
'language_id' => int 1
array (size=4)
'weight_class_title' =>
array (size=1)
'weight_class_title' => string 'tt' (length=2)
'weight_class_key' => string 'pound' (length=5)
'weight_class_id' => int 5
'language_id' => int 2
public function execute() {
$CLICSHOPPING_Language = Registry::get('Language');
$CLICSHOPPING_Db = Registry::get('Db');
$languages = $CLICSHOPPING_Language->getLanguages();
$QlastId = $CLICSHOPPING_Db->prepare('select weight_class_id
from :table_weight_classes
order by weight_class_id desc
limit 1');
$QlastId->execute();
$weight_class_id = $QlastId->valueInt('weight_class_id') + 1;
$weight_class_key = $_POST['weight_class_key'];
for ($i=0, $n=count($languages); $i<$n; $i++) {
$weight_class_title_array = $_POST['weight_class_title'];
$language_id = $languages[$i]['id'];
$weight_class_title_array = ['weight_class_title' => HTML::sanitize($weight_class_title_array[$language_id])];
$sql_data_array = ['weight_class_title' => $weight_class_title_array];
$insert_sql_data = ['weight_class_key' => $weight_class_key,
'weight_class_id' => $weight_class_id,
'language_id' => $languages[$i]['id']
];
$sql_data_array = array_merge($sql_data_array, $insert_sql_data);
$this->app->db->save('weight_classes', $sql_data_array);
}