SELECT 
  pfv.variant_id, 
  pfv.position, 
  pfvd.variant 
FROM 
  cscart_product_feature_variants AS pfv 
  INNER JOIN cscart_product_feature_variant_descriptions AS pfvd ON pfv.variant_id = pfvd.variant_id 
  AND pfvd.lang_code = 'en' 
WHERE 
  pfv.variant_id IN (
    84152, 87604, 84154, 87603, 87602, 87601, 
    84156, 84153, 87608, 87606, 87607, 
    87609, 87605, 87610, 87611, 87612, 
    87613, 84155, 87614, 87615, 87616, 
    87617, 87618, 87619, 87620
  )

Query time 0.00142

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "rows": 25,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (84152,87604,84154,87603,87602,87601,84156,84153,87608,87606,87607,87609,87605,87610,87611,87612,87613,84155,87614,87615,87616,87617,87618,87619,87620)"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "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": "pfvd.lang_code = 'en'"
        }
      }
    ]
  }
}