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 (
    68984, 68983, 68982, 68981, 68980, 68985, 
    68979, 69848, 69847, 69849, 70045, 
    70044, 70043, 70042, 70041, 70046, 
    70072, 70071, 70070, 70069, 70068, 
    70067, 70073, 70066, 70572, 70571, 
    70573, 70694, 70693, 70692, 70691, 
    70690, 70878, 70879, 71077, 71078, 
    73537, 73536, 74519, 74520, 74518, 
    74540, 74541, 74539, 78424, 78423, 
    78425, 78422, 81002, 81003, 81004, 
    81005, 81006, 81007, 82372, 82373, 
    82374, 82375, 83970, 83969, 83968, 
    83967, 83966, 83965, 83964, 85538, 
    85539, 85540, 85541, 86038, 86037, 
    86039, 86040, 86938, 86939, 86940, 
    86941, 86962, 86963, 86964, 86965, 
    86966, 86967, 86968, 86969
  )

Query time 0.01551

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": 85,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68984,68983,68982,68981,68980,68985,68979,69848,69847,69849,70045,70044,70043,70042,70041,70046,70072,70071,70070,70069,70068,70067,70073,70066,70572,70571,70573,70694,70693,70692,70691,70690,70878,70879,71077,71078,73537,73536,74519,74520,74518,74540,74541,74539,78424,78423,78425,78422,81002,81003,81004,81005,81006,81007,82372,82373,82374,82375,83970,83969,83968,83967,83966,83965,83964,85538,85539,85540,85541,86038,86037,86039,86040,86938,86939,86940,86941,86962,86963,86964,86965,86966,86967,86968,86969)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}