Multi-language advertising campaigns are a royal pain in the ass for copywriters.
Why? Because metaphors, puns and jokes are almost impossible to translate, and if copywriters aren't writing that sort of thing, we're carving out carefully manicured, short, sweet phrases with subtly shaded meanings and connotations in order to communicate days and days worth of thinking and meaning in 5 words or less... which also happen to be next to impossible to translate.
Here, for example, is a quick run down of various options for translating the wonderful word Schadenfreude. Especially good is the Thai: "I'm laughing at your bad luck," which also demonstrates the twin tendencies of inflated length and loss of coolness, post-translation process. For more LOLz, try babelfishing "guilty pleasure"... or pretty much any colloquialism you care to mention.
All this is bad enough when the text is translated by professional, human translators. But what usually happens is that it gets fed through a machine translation process, then tidied up by a person at the end. Unfortunately, that person is rarely included in the thought process behind the words, so all you get is a workaday, word-for-word translation, which usually completely misses the point, and occasionally makes such a balls of things that you might as well have asked the nearest 5 year old to do the job for you.
What's the solution? Get your translations done by copywriters who natively speak your target language! This has two drawbacks: price and process. It will cost a bomb, and you also have to think about it upfront and plan in a lot of extra time and work to make it come off successfully.
Most important is to make sure the thought behind the phrase to be translated gets to the translator, and that you get the original copy signed off by the client with plenty of time to spare.
Some bright spark has named this process "transcreation" which is kinda clumsy but gets the point across well enough until someone thinks of a better term. (Any offers?)
The alternative (read: more economical) route is to write a backup "safe line" to be used if all else fails. But, beware! If you go down this route, be prepared for the safe line to be the only copy that gets through, unless you have a great deal of patience and commitment (really, like years), a very forward thinking client who understands the above... and the internal agency connections and vision to pull it off.
More "woe is me" stuff about the trials of 21st century copywriting later...