I'm using Telerik version 2017 R2 for Winform app.
I followed this guide to localize all texts as well as labels in Composite Filter (custom filter) dialog, please see my result below
Composite Filter Localization result
As you see:
1. The texts in GREEN rectangle are localized successfully by adding the prefix "FR_".
2. The texts in RED rectangle are not localized because I don't know exactly the Localized String Id to override the default text.
Please advice! Thanks a lot!