PHP syntax highlight Can I install PHP plugin in RubyMine?

I love rubymine.  However, I have some projects which are Ruby/Rails/PHP combos.  When i look in the intellij plugin repository, I see a PHP plugin.
Should I be able to install this into rubymine?  All I really need is for syntax highlighting to work correctly in the editor :)

When I try to install the PHP plugin, i get an error saying I need another plugin "java-i18n..." which I cannot find.
Is there another way to get PHP syntax highlighting working in rubymine?
it doesnt work by default.  Rubymine covers so many other syntaxes it seems odd that PHP is missing