The Windows Phone team have just made 5 international style guides available for free download to help localize apps better.
"Style guides tell you how to "speak to" the user when addressing them in your app. For example, should you say "please" to the user? Or how do you abbreviate words for a smartphone screen, or what level of formality is appropriate (e.g., should you use "vous" or "tu" in French), or how do you translate "oops" so it's appropriate for a specific language."
To get started with making your app available in other languages, check the topic How to: Build a Localized Application for Windows Phone on MSDN. And, to find the right terminology and UI translations used in Windows Phone 7, use the Microsoft Language Portal online search.
For more in-depth reference material about building globalized apps for Windows Phone, visit the Globalization and Localization for Windows Phone pages on MSDN.
You'll also find more information about international Windows Phone 7 versions on the local Windows Phone 7 pages:
Here's the guides available for free download: (PDFs)
- German Windows Phone style guide
- English UK Windows Phone style guide
- French Windows Phone style guide
- Spanish Windows Phone style guide
- Italian Windows Phone style guide
PS: French Windows Phones say "Oups!" to express the meaning of "Oops!".