<Window xmlns:syncfusion="http://schemas.syncfusion.com/wpf">
    <Grid>
        <StackPanel>
            <TextBox 
                Text="Ths is a sampel text with speling errors."
                Name="textbox"
                TextWrapping="Wrap">
                
                <!--Attach SpellChecker to TextBox-->
                <syncfusion:SfSpellChecker.SpellChecker>
                    <syncfusion:SfSpellChecker 
                        x:Name="spellChecker"
                        EnableSpellCheck="True"/>
                </syncfusion:SfSpellChecker.SpellChecker>
            </TextBox>
            
            <Button 
                Content="Spell Check"
                Click="SpellCheck_ButtonClick"
                HorizontalAlignment="Center"/>
        </StackPanel>
    </Grid>
</Window>

// Code-behind
private void SpellCheck_ButtonClick(object sender, RoutedEventArgs e)
{
    spellChecker.PerformSpellCheckUsingDialog();
}

<syncfusion:SfSpellChecker 
    x:Name="spellChecker"
    EnableSpellCheck="True"
    EnableContextMenu="True"/>

// Create spell checker instance
SfSpellChecker spellChecker = new SfSpellChecker();
spellChecker.EnableSpellCheck = true;

// Attach to TextBox
SfSpellChecker.SetSpellChecker(textbox, spellChecker);

// Open spell check dialog
spellChecker.PerformSpellCheckUsingDialog();

SfSpellChecker spellChecker = new SfSpellChecker();
spellChecker.EnableSpellCheck = true;
spellChecker.EnableContextMenu = true;

// Configure ignore options
spellChecker.IgnoreUrl = true;
spellChecker.IgnoreEmailAddress = true;
spellChecker.IgnoreUpperCaseWords = true;

SfSpellChecker.SetSpellChecker(textbox, spellChecker);

// Create culture-specific spell checker
CultureInfo culture = new CultureInfo("fr-FR");
SfSpellChecker spellChecker = new SfSpellChecker();

// Add French dictionary
spellChecker.Dictionaries = new DictionaryCollection();
spellChecker.Dictionaries.Add(
    new HunspellDictionary()
    {
        Culture = culture,
        GrammarUri = new Uri("/MyApp;component/Dictionaries/fr-FR.aff", UriKind.Relative),
        DictionaryUri = new Uri("/MyApp;component/Dictionaries/fr-FR.dic", UriKind.Relative)
    }
);

spellChecker.Culture = culture;
SfSpellChecker.SetSpellChecker(textbox, spellChecker);

// Add custom words dictionary
Uri customDictUri = new Uri(Directory.GetCurrentDirectory() + 
                           @"\Dictionaries\CustomWords.txt", UriKind.Absolute);

spellChecker.Dictionaries.Add(
    new CustomDictionary()
    {
        Culture = new CultureInfo("en-US"),
        DictionaryUri = customDictUri
    }
);

spellChecker.SpellCheckCompleted += (sender, e) =>
{
    // Suppress default message box
    (e as SpellCheckCompletedEventArgs).ShowMessageBox = false;
    
    // Custom completion logic
    MessageBox.Show("Spell check completed!", "Done");
};