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 = 'vi' 
WHERE 
  pfv.feature_id IN (
    21384, 25127, 23540, 24831, 24957, 21386, 
    24144, 25095, 19725, 24832, 20381, 
    21914, 20084, 20083, 24974, 23209, 
    21594, 19747, 23527, 23526, 23528, 
    21596
  ) 
  AND pfv.product_id IN (
    1896, 50216, 35256, 47632, 48823, 1894, 
    49873, 6357, 47597, 18608, 1057, 17265, 
    17259, 48980, 31729, 1538, 15322, 35167, 
    35166, 35169, 1535
  ) 
  AND pfv.lang_code = 'vi'

Query time 0.04699

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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": "PRIMARY",
          "key_length": "6",
          "used_key_parts": ["feature_id", "product_id"],
          "rows": 490,
          "filtered": 0.079303443,
          "attached_condition": "pfv.feature_id in (21384,25127,23540,24831,24957,21386,24144,25095,19725,24832,20381,21914,20084,20083,24974,23209,21594,19747,23527,23526,23528,21596) and pfv.product_id in (1896,50216,35256,47632,48823,1894,49873,6357,47597,18608,1057,17265,17259,48980,31729,1538,15322,35167,35166,35169,1535) and pfv.lang_code = 'vi'",
          "using_index": true
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "feature_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "ref": ["dev_db.pfv.variant_id"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "fv.feature_id = pfv.feature_id"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["dev_db.pfv.variant_id", "const"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "fvd.lang_code = 'vi'"
        }
      }
    ]
  }
}