Translating your WP7 Apps
Why translate your app? for starters you will increase your downloads quite considerably. The english market seems to be swamped with a dozen apps that all seem to do the same thing and therefore publishing to markets where there may be no local competition or very little puts you in good standings.
Proof? well here are some download stats from one of my apps “Free Wikipedia Viewer” by top 5 countries which you can guess what languages they speak. As you can see only 2 of the top 5 speak english, this I have found across most of my apps, english is often not the highest number of downloads
Germany 3,381
Italy 2,610
Australia 1,027
France 950
United States 903
For my market place publishing descriptions I use a professional transcription service http://www.translia.com/ which costs me around 9 cents a word and I get it translated to german, french, italian and spanish. Generally it comes in at around 20 pounds per app so it is not a big cost. For the internal words in the app I use resx files and have been modifying a translating tool from one I got from codeplex a long time ago to do translations specially for wp7 Apps.
So in the spirit of giving back to the community I have uploaded the tool I currently use to translate my apps to codeplex at http://wp7resxlocgenerator.codeplex.com/
Hopefully all the instructions you need to translate your apps are on codeplex, if not just ask as i know it works for me!
Apporista 
Thank you so much for posting this!. I’ve been thinking about trying to localize my app but it always looked so daunting. I do have one question, when you submit it how do you fill in the languages section? Do you choose English(International) or do you choose all the languages it supports? I’m probably over-thinking this.
English(International) and it will detect the other languages you have in your xap file, at the moment marketplace will only detect german, spanish, french and italian but make sure you remember to set the supported cultures tag in your project .csproj file, you may have to use notepad to edit it. I use my tool and generally export to the below values.
af;ar;be;bg;ca;cs;da;de;el;es;et;fa;fi;fil-PH;fr;gl;hu;hr;id;is;it;ja;ko;lt;lv;mk;ms;nl;no;pl;pt;ro;ru;sk;sl;sq;sv;sr;th;tr;uk;vi;zh-CN;zh-Hans;zh-Hant;zh-TW