SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '4793', '4786', '4764', '4790', '3953', 
    '4792', '4777', '4778', '4766', '4783', 
    '4773', '4799', '4779', '4810', '4776', 
    '4780', '4806', '4782', '4784', '4797', 
    '3745', '3719', '1938', '3709', '4754', 
    '4862', '1978', '1934', '4753', '4867', 
    '1912', '1895', '1858', '1862', '4755', 
    '4879', '5162', '1939', '2970', '1987', 
    '1970', '1941', '5137', '2144', '1870', 
    '1859', 'Y'
  ) 
  AND lang_code = 'en'

Query time 0.00094

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": 47,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('4793','4786','4764','4790','3953','4792','4777','4778','4766','4783','4773','4799','4779','4810','4776','4780','4806','4782','4784','4797','3745','3719','1938','3709','4754','4862','1978','1934','4753','4867','1912','1895','1858','1862','4755','4879','5162','1939','2970','1987','1970','1941','5137','2144','1870','1859','Y') and cscart_product_feature_variant_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}