To reproduce:

Add a RadSpellChecker and a RadTextBox. Load a custom dictionary for RadTextBox:

DocumentSpellCheckerspellChecker = checker.GetControlSpellChecker(typeof(RadTextBox)).SpellChecker asDocumentSpellChecker;

WordDictionarydict = newWordDictionary();



using(MemoryStreamms = newMemoryStream(File.ReadAllBytes("sv-SE.tdf")))
{
           dict.Load(ms);
}

spellChecker.AddDictionary(dict, CultureInfo.CurrentCulture);

On a button click spell check the textbox when it has the following text: Varfor fungärar innte dettta

this.checker.SpellCheckMode = SpellCheckMode.AllAtOnce;

this.checker.Check(this.textBox);

You will see that the suggested words are not in Swedish.

Workaround:

Add the dictionary to the RadRichTextBox spell checker:

DocumentSpellCheckerrichSpellChecker = checker.GetControlSpellChecker(typeof(RadRichTextBox)).SpellChecker asDocumentSpellChecker;

richSpellChecker.AddDictionary(dict, CultureInfo.CurrentCulture);