SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '4796', '4793', '3953', '4766', '4803', 
    '4763', '4800', '4808', '4783', '4801', 
    '4787', '4773', '4799', '4779', '4776', 
    '4780', '4809', '4806', '4781', '4782', 
    '4784', '4789', '4797', '2051', '2933', 
    '1938', '3709', '2037', '1978', '2273', 
    '2375', '2613', '1858', '1862', '2349', 
    '1855', '1996', '5115', '1987', '1970', 
    '2711', '3748', '2004', '5137', '2499', 
    '1993', '3101', '3095', '1510', '1620', 
    '1297', '1143', '1777', '167', '1240', 
    '534', '1619', '113', '16', '63', '851', 
    '1618', '1269', '165', '1753', '878', 
    '1243', '3698', '1778', '169', '1851', 
    '3382', '221', '1381', '500', '1573', 
    '548', '1754', '1387', '222', '3378', 
    '391', '1793', '1436', '378', '2030', 
    '1870', '1859', 'Y', '1615'
  ) 
  AND lang_code = 'en'

Query time 0.00808

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variant_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "rows": 90,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('4796','4793','3953','4766','4803','4763','4800','4808','4783','4801','4787','4773','4799','4779','4776','4780','4809','4806','4781','4782','4784','4789','4797','2051','2933','1938','3709','2037','1978','2273','2375','2613','1858','1862','2349','1855','1996','5115','1987','1970','2711','3748','2004','5137','2499','1993','3101','3095','1510','1620','1297','1143','1777','167','1240','534','1619','113','16','63','851','1618','1269','165','1753','878','1243','3698','1778','169','1851','3382','221','1381','500','1573','548','1754','1387','222','3378','391','1793','1436','378','2030','1870','1859','Y','1615') and cscart_product_feature_variant_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}

Result

variant_id yml2_unit
16
63
113
165
167
169
221
222
378
391
500
534
548
851
878
1143
1240
1243
1269
1297
1381
1387
1436
1510
1573
1615
1618
1619
1620
1753
1754
1777
1778
1793
1851
1855
1858
1859
1862
1870
1938
1970
1978
1987
1993
1996
2004
2030
2037
2051
2273
2349
2375
2499
2613
2711
2933
3095
3101
3378
3382
3698
3709
3748
3953
4763
4766
4773
4776
4779
4780
4781
4782
4783
4784
4787
4789
4793
4796
4797
4799
4800
4801
4803
4806
4808
4809
5115
5137