The Machine Translation Equilibrium
translationparty.com
translationparty.com
If we take a list of all found equilibrium expressions and have a human translator eliminate the ones that have different meanings in the source and destination languages, we'll have a list of phrases that can be transmitted safely through google translate.
A phrasebook like that would be worth a lot, to me at least. Two applications where a phrasebook might be good enough are tourism and freelance web development.
edit: Here's a great example "The problem is Internet Explorer 6 support." (assuming that means something vaguely similar in the Japanese version, of course)
A time-honored classic.
Additionally, I'm not sure your example, "i am a boy but not a girl", parses in English. Being a boy does not normally make one a girl, so wouldn't "...and not a girl" make more sense?
The above mentioned phrase actually reaches an oscillatory state, which is kind of cool.