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 (
    84386, 84387, 84388, 84389, 84390, 84391, 
    84392, 84393, 84394, 84395, 84396, 
    84397, 84398, 84399, 84400, 84426, 
    84427, 84428, 84429, 86327, 86326, 
    86840, 86841
  )

Query time 0.00089

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": 23,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (84386,84387,84388,84389,84390,84391,84392,84393,84394,84395,84396,84397,84398,84399,84400,84426,84427,84428,84429,86327,86326,86840,86841)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}