Super article by the WikiMedia Foundation engineering folks about Designing for the Multilingual Web using the Wikipedia Universal Language Selector user interface as an example. Great ideas about tools that are available, as well as covering the basics of wireframing (mockups), prototyping, and user testing. Lots of inspiration there for developers and builders of apps who want to ensure their user experience (UX) really delivers for a global audience.
Check out the use of the Firefox-based Pencil, how to translate your mockups, and how to perform remote user testing using Google+ Hangouts.
Paul Giner demonstrates how to translate mockups.
A little clunky and homespun in parts (I would prefer if tools such as Pencil or Balsamiq MockUps, and so on, could roundtrip directly from SVG to XLIFF for example, and Pencil doesn't work yet with the latest versions for Firefox) and I am not sure how it can really scales to enterprise-level use. However, the UX methodology is basically sound, and reinforces the importance of designing and testing in more that one language. The most powerful message for me is that you do not need special resources, training or expensive tools to deliver great-looking usable apps if you're a developer.
Definitely worth considering if you're building apps out there in the community.