SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  fv.position, 
  fvd.variant 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_feature_variants AS fv ON pfv.feature_id = fv.feature_id 
  AND pfv.variant_id = fv.variant_id 
  INNER JOIN cscart_product_feature_variant_descriptions AS fvd ON pfv.variant_id = fvd.variant_id 
  AND fvd.lang_code = 'en' 
WHERE 
  pfv.feature_id IN (2, 6) 
  AND pfv.product_id IN (
    584, 573, 561, 556, 553, 549, 545, 541, 
    525, 521, 517, 513, 507, 497, 492, 489, 
    486, 482, 455, 453, 452, 451, 450, 449, 
    448, 447, 446, 445, 444, 443, 442, 394, 
    378, 217
  ) 
  AND pfv.lang_code = 'en'

Query time 0.00183

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "51.86"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "idx_product_feature_variant_id",
          "used_key_parts": [
            "product_id",
            "feature_id",
            "lang_code"
          ],
          "key_length": "12",
          "rows_examined_per_scan": 68,
          "rows_produced_per_join": 68,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "7.73",
            "eval_cost": "6.80",
            "prefix_cost": "14.53",
            "data_read_per_join": "52K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ],
          "attached_condition": "((`betaatif_store`.`pfv`.`feature_id` in (2,6)) and (`betaatif_store`.`pfv`.`product_id` in (584,573,561,556,553,549,545,541,525,521,517,513,507,497,492,489,486,482,455,453,452,451,450,449,448,447,446,445,444,443,442,394,378,217)) and (`betaatif_store`.`pfv`.`lang_code` = 'en'))"
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "feature_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "betaatif_store.pfv.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 38,
          "filtered": "56.86",
          "cost_info": {
            "read_cost": "17.00",
            "eval_cost": "3.87",
            "prefix_cost": "38.33",
            "data_read_per_join": "44K"
          },
          "used_columns": [
            "variant_id",
            "feature_id",
            "position"
          ],
          "attached_condition": "(`betaatif_store`.`fv`.`feature_id` = `betaatif_store`.`pfv`.`feature_id`)"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "betaatif_store.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 38,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "9.67",
            "eval_cost": "3.87",
            "prefix_cost": "51.86",
            "data_read_per_join": "116K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}