SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '5898', '1449', '1201', '1219', '5899', 
    '1283', '1281', '1257', '5902', '5904', 
    '5905', '5906', '5907', '5908', '1282', 
    '1425', '1313', '1280', '5909', '1314', 
    '1200', '5910', '5912', '1198', '1199', 
    '5914', '1241', '5916'
  ) 
  AND lang_code = 'ru'

Query time 0.00052

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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": 28,
      "filtered": 100,
      "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('5898','1449','1201','1219','5899','1283','1281','1257','5902','5904','5905','5906','5907','5908','1282','1425','1313','1280','5909','1314','1200','5910','5912','1198','1199','5914','1241','5916') and cscart_product_feature_variant_descriptions.lang_code = 'ru'"
    }
  }
}