SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1', '3', '125', '296', '258', '127', 
    '149', '120', '123', '234', '146', 
    '57', '147', '31', '26', '267', '298', 
    '262', '263', '264', '265', '260', 
    '299', '237', '238', '154'
  ) 
  AND lang_code = 'ru'

Query time 0.00046

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.21"
    },
    "table": {
      "table_name": "cscart_product_feature_variant_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "variant_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 26,
      "rows_produced_per_join": 26,
      "filtered": "100.00",
      "index_condition": "((`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('1','3','125','296','258','127','149','120','123','234','146','57','147','31','26','267','298','262','263','264','265','260','299','237','238','154')) and (`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "15.61",
        "eval_cost": "2.60",
        "prefix_cost": "18.21",
        "data_read_per_join": "81K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}