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 (
    68341, 68340, 68339, 68338, 68342, 70085, 
    70086, 70084, 71140, 71139, 71138, 
    71137, 71136, 71135, 71134, 71141, 
    74807, 74808, 78516, 78515, 79230, 
    79231, 79229, 81215, 81223, 81222, 
    81221, 81220, 81219, 81218, 81217, 
    81216, 81505, 81506, 81507, 81508, 
    81679, 81683, 81684, 74389, 82449, 
    82450, 74391, 74392, 74393, 74394, 
    74395, 74396, 74397, 74399, 84396, 
    84397, 84398, 84399, 84400, 84434, 
    84435, 84436, 84437, 84438, 84439, 
    84468, 84462, 84469, 84470, 84467, 
    84465, 84466, 84464, 84463
  )

Query time 0.00708

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": 70,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68341,68340,68339,68338,68342,70085,70086,70084,71140,71139,71138,71137,71136,71135,71134,71141,74807,74808,78516,78515,79230,79231,79229,81215,81223,81222,81221,81220,81219,81218,81217,81216,81505,81506,81507,81508,81679,81683,81684,74389,82449,82450,74391,74392,74393,74394,74395,74396,74397,74399,84396,84397,84398,84399,84400,84434,84435,84436,84437,84438,84439,84468,84462,84469,84470,84467,84465,84466,84464,84463)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}