SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1', '1292', '1310', '1299', '1305', 
    '1302', '1311', '1280', '1281', '1312', 
    '1306', '1223', '1226', '1224', '1199', 
    '1201'
  ) 
  AND lang_code = 'ru'

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "38.41"
    },
    "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": 16,
      "rows_produced_per_join": 16,
      "filtered": "100.00",
      "index_condition": "((`cscart`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('1','1292','1310','1299','1305','1302','1311','1280','1281','1312','1306','1223','1226','1224','1199','1201')) and (`cscart`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "35.21",
        "eval_cost": "3.20",
        "prefix_cost": "38.41",
        "data_read_per_join": "49K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}