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 (
    21226, 21019, 21038, 21025, 19997, 20318, 
    21626, 21016, 19661, 24707, 24708, 
    20637, 20002, 21026, 19682, 24056, 
    22406, 21223, 24045
  ) 
  AND pfv.product_id IN (
    2135, 2507, 21065, 2501, 5568, 4305, 
    23162, 2510, 6533, 46739, 3447, 16601, 
    2500, 6466, 40153, 306, 2138, 40143
  ) 
  AND pfv.lang_code = 'vi'

Query time 0.04625

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": 371,
          "filtered": 0.035409119,
          "attached_condition": "pfv.feature_id in (21226,21019,21038,21025,19997,20318,21626,21016,19661,24707,24708,20637,20002,21026,19682,24056,22406,21223,24045) and pfv.product_id in (2135,2507,21065,2501,5568,4305,23162,2510,6533,46739,3447,16601,2500,6466,40153,306,2138,40143) 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'"
        }
      }
    ]
  }
}