It could be up to 30 percent longer. If you had visions of creating your marketing piece in other languages besides English, remember, the length of the translated copy might be longer (or shorter) than the English. This will affect the design of the document, and to preserve the design, you might have to edit the translation, as well as the English.
Here are a few estimations of language length (which depends on the nature of the text and the topic) when translating from English:*
Spanish: 25% to 30% longer
French: 15% to 25% longer
Russian: about 30% shorter
Asian languages: as much as 40% shorter
So if you want to create a promotional button, for example, in a number of languages, keep in mind how much space you have on that button to do so successfully.