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 = 'vi' 
WHERE 
  pfv.variant_id IN (
    68392, 68391, 68390, 68393, 68389, 69618, 
    69617, 69622, 69621, 71557, 71556, 
    71913, 71912, 73307, 73306, 73309, 
    73308, 74986, 74985, 74984, 74983, 
    74987, 75523, 75524, 76709, 76708, 
    76707, 76710, 76741, 76740, 76742, 
    77936, 77934, 77935, 77945, 77943, 
    77944, 78651, 79378, 79377, 68258, 
    81479, 81480, 83205, 83206, 83207, 
    83208, 83209, 86166, 86167
  )

Query time 0.00662

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": 50,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68392,68391,68390,68393,68389,69618,69617,69622,69621,71557,71556,71913,71912,73307,73306,73309,73308,74986,74985,74984,74983,74987,75523,75524,76709,76708,76707,76710,76741,76740,76742,77936,77934,77935,77945,77943,77944,78651,79378,79377,68258,81479,81480,83205,83206,83207,83208,83209,86166,86167)"
        }
      },
      {
        "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 = 'vi'"
        }
      }
    ]
  }
}