I could save the key, then I only had a fixed text with no variables, but I could not save this text for instance:
<br /><button class="bx-btn bx-hide-when-logged-in bx-def-margin-top" onclick="document.location='{0}'">Become a member now!</button>
From my side, it is strored in the lang keys fine. The only this that this class "bx-hide-when-logged-in" shows the button only for guests.