In views/elements/install.thtml there are a few lines similar to: sprintf(_($buttonMessage),$_install_platform_string) This isn't going to work because $buttonMessage is a variable and needs to be a string so gettext can pick it up. It's working right now because the string a_install is left over from a while ago, but gettext is trying to deprecate it now because it's not used anywhere that it can see.
Good catch. If we need to assign gettext strings to a variable, we should always keep intact the _('some_static_text') pattern because the gettext tools read the code files statically.
This is fixed since r11552.