Gephi uses GitHub to host the source code and track issues. The trunk repository is the most up-to-date version but may be unstable. The last stable version is located in the release tab on GitHub.
Localization is available in French, Spanish, Japanese, Brazilian Portuguese, Russian, Chinese, Czech, German and Romanian. In Gephi, simply go to Tools -> Languages to switch.
Web/Internet, Social Networks, Biological Networks, Infrastructures and others…
If you are looking for data samples to test Gephi, look at the wiki.