SELECT 
  b.variant_name, 
  a.* 
FROM 
  cscart_product_option_variants AS a 
  LEFT JOIN cscart_product_option_variants_descriptions AS b ON b.variant_id = a.variant_id 
  AND b.lang_code = 'en' 
WHERE 
  1 
  AND a.option_id IN (120) 
  AND a.status = 'A' 
ORDER BY 
  a.position, 
  a.variant_id

Query time 0.00084

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.70"
    },
    "ordering_operation": {
      "using_filesort": true,
      "nested_loop": [
        {
          "table": {
            "table_name": "a",
            "access_type": "ref",
            "possible_keys": [
              "status",
              "option_id",
              "option_id_2"
            ],
            "key": "option_id",
            "used_key_parts": [
              "option_id",
              "status"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "0.10",
              "prefix_cost": "0.35",
              "data_read_per_join": "48"
            },
            "used_columns": [
              "variant_id",
              "option_id",
              "position",
              "modifier",
              "modifier_type",
              "weight_modifier",
              "weight_modifier_type",
              "point_modifier",
              "point_modifier_type",
              "status"
            ]
          }
        },
        {
          "table": {
            "table_name": "b",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "variant_id",
              "lang_code"
            ],
            "key_length": "9",
            "ref": [
              "s2cart.a.variant_id",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.25",
              "eval_cost": "0.10",
              "prefix_cost": "0.70",
              "data_read_per_join": "784"
            },
            "used_columns": [
              "variant_id",
              "lang_code",
              "variant_name"
            ]
          }
        }
      ]
    }
  }
}