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 (
    81610, 81619, 81620, 81611, 81612, 81613, 
    81614, 81615, 81616, 81617, 81601, 
    81602, 81603, 81604, 81605, 81606, 
    81607, 81608, 81609, 81621, 81622, 
    81623, 81624, 81625, 81626, 81627, 
    81628, 86729, 86725, 86731, 86728, 
    86730, 86727, 86726
  )

Query time 0.00395

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": 34,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (81610,81619,81620,81611,81612,81613,81614,81615,81616,81617,81601,81602,81603,81604,81605,81606,81607,81608,81609,81621,81622,81623,81624,81625,81626,81627,81628,86729,86725,86731,86728,86730,86727,86726)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}