SELECT 
  cscart_product_files.*, 
  cscart_product_file_descriptions.file_name, 
  cscart_product_file_descriptions.license, 
  cscart_product_file_descriptions.readme 
FROM 
  cscart_product_files 
  LEFT JOIN cscart_product_file_descriptions ON cscart_product_file_descriptions.file_id = cscart_product_files.file_id 
  AND cscart_product_file_descriptions.lang_code = 'en' 
WHERE 
  1 = 1 
  AND cscart_product_files.product_id = 230 
  AND preview_path != '' 
  AND cscart_product_files.status = 'A' 
ORDER BY 
  cscart_product_files.position asc, 
  cscart_product_file_descriptions.file_name asc

Query time 0.00102

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.0051722,
    "filesort": {
      "sort_key": "cscart_product_files.position, cscart_product_file_descriptions.file_name",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_files",
              "access_type": "ref",
              "possible_keys": ["product_id"],
              "key": "product_id",
              "key_length": "3",
              "used_key_parts": ["product_id"],
              "ref": ["const"],
              "loops": 1,
              "rows": 1,
              "cost": 0.00345856,
              "filtered": 100,
              "attached_condition": "cscart_product_files.preview_path <> '' and cscart_product_files.`status` = 'A'"
            }
          },
          {
            "table": {
              "table_name": "cscart_product_file_descriptions",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["file_id", "lang_code"],
              "ref": ["u985510652_ecartify.cscart_product_files.file_id", "const"],
              "loops": 1,
              "rows": 1,
              "cost": 0.00171364,
              "filtered": 100,
              "attached_condition": "trigcond(cscart_product_file_descriptions.lang_code = 'en')"
            }
          }
        ]
      }
    }
  }
}