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 (
    81976, 81977, 85544, 85545, 85546, 85547, 
    85695, 85696, 86589, 86585, 86588, 
    86586, 86587, 86653, 86652, 86788, 
    86787, 86786, 86796, 86797, 86798, 
    87011, 87012, 87013, 87894, 87895, 
    87896
  )

Query time 0.00397

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": 27,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (81976,81977,85544,85545,85546,85547,85695,85696,86589,86585,86588,86586,86587,86653,86652,86788,86787,86786,86796,86797,86798,87011,87012,87013,87894,87895,87896)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}