SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '5495', '5456', '4422', '4852', '5335', 
    '4305', '2219', '1305', '2061', '1391', 
    '1669', '1293', '2064', '2062', '2292', 
    '1315', '1397', '1969', '2099', '2063', 
    '1265', '2007', '2508', '1392', '1365', 
    '2160', '2156', '1444', '2066', '2592', 
    '1398', '1275', '1248', '2330', '1227', 
    '2467', '1242', '1402', '2386', '2065', 
    '2158', '1345', '1249', '1405'
  ) 
  AND lang_code = 'ru'

Query time 0.00102

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "30.81"
    },
    "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": 44,
      "rows_produced_per_join": 44,
      "filtered": "100.00",
      "index_condition": "((`unicomps`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('5495','5456','4422','4852','5335','4305','2219','1305','2061','1391','1669','1293','2064','2062','2292','1315','1397','1969','2099','2063','1265','2007','2508','1392','1365','2160','2156','1444','2066','2592','1398','1275','1248','2330','1227','2467','1242','1402','2386','2065','2158','1345','1249','1405')) and (`unicomps`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "26.41",
        "eval_cost": "4.40",
        "prefix_cost": "30.81",
        "data_read_per_join": "137K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}