Thank you for contacting us. I've tested the mentioned scenario and everything works fine on my side when the text file is encoded with UTF8. If the file is using some other encoding, the UTF8 that's used in the StreamReader's constructor will not be able to read all symbols correctly. Could you check if your file is using UTF8 encoding?
I'm sending you my test project and the test file - as you can see the symbols are shown correctly when you search inside RadAutoCompleteBox's items.
I'm looking forward to hearing from you.
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