I read that in order to enable mnemonics, I have to turn on RecognizesAccessKey on ContentPresenter.
When I tried this code, I saw only text without button.
<Button x:Name="OkButton" Content="_OK" Command="{Binding ExecuteCommand}">
<Button.Template>
<ControlTemplate TargetType="Button">
<ContentPresenter RecognizesAccessKey="True" />
</ControlTemplate>
</Button.Template>
</Button>
Probably there's a way to change it without deleting button's default template?