Sisulizer found an XAML component that has no name attribute. This kind on component can be localized but it may be that its context will change if you add another similar component on the form. This is why it is recommended that you give a name attribute to each component you have.
A name attribute is either x:Uid, x:Name or Name attribute. For example if you have the following menu component.
<Menu> ... </Menu>
Add a name attribute.
<Menu x:Uid="MainMenu"> ... </Menu>
or
<Menu x:Name="MainMenu"> ... </Menu>
or
<Menu Name="MainMenu"> ... </Menu>
Read more about WPF localization.