SELECT 
  search_phrases 
FROM 
  cscart_ab__search_motivation 
WHERE 
  category_id = 388 
  AND lang_code = 'it'

Query time 0.00046

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.20"
    },
    "table": {
      "table_name": "cscart_ab__search_motivation",
      "access_type": "ref",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "category_id"
      ],
      "key_length": "3",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 0,
      "filtered": "10.00",
      "index_condition": "(`eshopuga_upgr_4122`.`cscart_ab__search_motivation`.`lang_code` = 'it')",
      "cost_info": {
        "read_cost": "1.00",
        "eval_cost": "0.02",
        "prefix_cost": "1.20",
        "data_read_per_join": "3"
      },
      "used_columns": [
        "category_id",
        "lang_code",
        "search_phrases"
      ]
    }
  }
}