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 (
    68399, 68398, 68400, 71148, 71147, 71146, 
    71145, 71144, 71143, 71142, 71149, 
    71441, 71440, 71442, 71443, 71862, 
    71861, 71860, 71863, 73579, 73578, 
    76046, 76695, 76694, 76696, 77409, 
    77410, 78799, 78798, 78797, 78800, 
    78822, 78821, 78820, 78819, 78818, 
    78817, 78816, 78823, 86457, 86456, 
    86455, 86454, 86606, 86607, 86608
  )

Query time 0.00199

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": 46,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68399,68398,68400,71148,71147,71146,71145,71144,71143,71142,71149,71441,71440,71442,71443,71862,71861,71860,71863,73579,73578,76046,76695,76694,76696,77409,77410,78799,78798,78797,78800,78822,78821,78820,78819,78818,78817,78816,78823,86457,86456,86455,86454,86606,86607,86608)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}