We\'re getting ready to translate our PHP website into various languages, and the gettext support in PHP looks like the way to go.
All the tutorials I see recommend
I'd go so far as to say that you never (for most values of never) want to use free text as keys to anything. Imagine if SO used the query title as key to this page for instance. If someone links to it, and then the title is edited, the link is no longer valid.
Your problem is similar, except you would also be responsible for updating all links...
Like Douglas Leeder mentions, what you probably want to do is use English as the default (backup) language, although an interface that uses English and another language intermixed is highly confusing (but mildly amusing, too).