Many weeks ago I started the task of translating Hudson to Spanish.
Although it is a hard work it has helped me to know and understand all the corners of this awesome CI application.
Instead of having an unique repository of key-values pairs, Hudson has hundreds of internationalizable files distributed along the sources which you have to copy and edit by hand, making the work very heavy.
This was the reason why I decided to code a small tool: translation-tool.pl which has helped me a lot, and which is able to look for missing keys and files, print statistics about the progress, batch edition, and much more.
Another problem in translating an application is to find the adequate words in your language to express the original idea; for instance the words `build`, `Dashboard`, `fingerprint` in English sound weird in Spanish for this context. I have written a wiki page with the status of the Spanish translation where people can leave their opinions and suggestions, so if you speak Spanish, please feel free to collaborate.