Perhaps one way to make such a tool would be to try replacing each word with one of its synonyms but that wouldn't change the form of the sentence.
I thought at first that it might be worth using Google Translate (or Bing, etc.) to translate a sentence from English into a language and back again. I was surprised to find that most of the results are grammatically incorrect and at least one, while almost grammatically correct, has a quite different meaning (Eng. -> Latin -> Eng.).
And unfortunately there wasn't much variation to be seen either.
It seems that the verb to be is easily mangled and that some languages seem to require a definite article where the original English does not.
Original English: It's actually quite rare for sentences to not be unique.
Spanish: En realidad es bastante raro para frases para no ser único.
Back to English: It's actually quite rare for phrases not to be unique.
German: Es ist eigentlich ziemlich selten für Sätze nicht einzigartig sein.
Back to English: It's actually quite rare for phrases not to be unique.
Japanese: 文章は一意ではないことは実際には非常にまれです。
Back to English: Sentence is very rare in practice is not unique.
French: Il est en fait assez rare pour les phrases à ne pas être unique.
Back to English: It is actually quite rare for phrases not to be unique.
Polish: To rzeczywiście dość rzadko zdania nie być unikalna.
Back to English: It's actually quite rare sentence not be unique.
Hebrew: זה בעצם די נדיר משפטים לא להיות ייחודיים.
Back to English: It's actually quite rare sentences not be unique.
Italian: In realtà è abbastanza raro per le frasi di non essere unico.
Back to English: It's actually quite rare for the sentences not to be unique.
Latin (but which era?): Suus 'vere non esse unica sententia admodum rarum.
Back to English: It's really not very rare, is a single sentence.
Romanian (which some say is similar to Latin!): Este de fapt destul de rar pentru fraze să nu fie unic.
Back to English: It's actually quite rare for phrases is not unique.