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 (
    81215, 81223, 81222, 81221, 81220, 81219, 
    81218, 81217, 81216, 84434, 84435, 
    84436, 84437, 84438, 84439, 84468, 
    84462, 84469, 84470, 84467, 84465, 
    84466, 84464, 84463, 85607, 85608, 
    85609, 86290, 86291, 86292, 86293
  )

Query time 0.02384

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": 31,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (81215,81223,81222,81221,81220,81219,81218,81217,81216,84434,84435,84436,84437,84438,84439,84468,84462,84469,84470,84467,84465,84466,84464,84463,85607,85608,85609,86290,86291,86292,86293)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}