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 (
    68206, 68205, 75520, 75519, 81005, 81002, 
    81004, 81003, 81006, 81007, 81883, 
    82583, 82582, 82584, 82585, 82581, 
    82580, 82579, 82578, 82590, 82577, 
    82586, 82587, 82589, 82588, 82591, 
    82599, 82596, 82597, 82598, 82593, 
    82594, 82595, 82600, 82601, 82592, 
    84349, 84348, 84347, 84426, 84427, 
    84428, 84429, 85929, 85930, 86299, 
    86298, 86297, 87124, 87458, 87457
  )

Query time 0.00659

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": 51,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68206,68205,75520,75519,81005,81002,81004,81003,81006,81007,81883,82583,82582,82584,82585,82581,82580,82579,82578,82590,82577,82586,82587,82589,82588,82591,82599,82596,82597,82598,82593,82594,82595,82600,82601,82592,84349,84348,84347,84426,84427,84428,84429,85929,85930,86299,86298,86297,87124,87458,87457)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}