When you translate a document, you go from the beginning to the end and all the time, you have an overview of the full document. The difference with localization is that you only have a partial view of the file you're working on and it's completely out of context (you don't translate the dialog box straight in the UI ;-). This is the major difficulty in localization, the lack of context with the strings you manipulate. But, but stay tuned, we use several tools that fills this gap.

So localization means translating each string that appears in the user interface or the help within the product. The file format we are using is .po and the main tool that serve both to translate or as a repository is Pootle. See here for an overview of the tool: https://translations.documentfoundation.org/. Pootle is very friendly tool, easy to use and to manage. Thanks to the Pootle development team, it's more and more adapted to the diversity of our community. The team is very responsive when you meet an issue and often listen to our request for enhancement. LibreOffice is a very large product, containing many, many strings either in the UI (92464 words) and in the help (439921 words), handling all this in so many languages is a real challenge.

If you're not used to localization, the best way is to ask for a reviewer status on Pootle. It will allow you to make suggestions, to get used to the way the files are organized and to their content. There is variables you have to take care and for the help files, they are in xml, so the tags are sometimes disturbing. To get this rights on Pootle, ask to your language team on the relevant language list, or come to the international mailing list at l10 <at> global.libreoffice.org. You also need to have the last LibreOffice version installed in order to check about the strings in the UI or the help. Note that the l10n list is dedicated to localization. Our teams are very small most of the time, and our time is as precious as yours, so if you have a question about translation, ask it on the projects <at> global.libreoffice.org list, it's a dedicated list for cross communication in the community. In any case, don't feel shy if you find it complicated, we all make and made mistakes, it's a good way to learn :-)

If you have already done localization, you might want to be able to translate directly. Again, ask on the relevant language list or to the l10n list for such rights. Each team have his own organization depending on its size. For French for example, I'm alone so I never check for suggestions on Pootle and may overwrite them if somebody have tried to help me and didn't inform me. So whatever you want to do, inform the person in charge. You'll find all the names listed here: http://wiki.documentfoundation.org/Language_Teams.

If nobody is in charge, or if it's a new language you want to add to the product, please see how to do so following this guide: http://wiki.documentfoundation.org/LibreOffice_Localization_Guide. Don't feel impressed by the length of the article or some technical parts, we are all here to help you and we have a magician with us better known as Andras Timar :-) He is the one who update the templates for us, integrate our work in the branch, take care of Pootle and together with Rimas Kudelis, solve many of our headaches.

Once you are ready to translate, you can either do it directly on Pootle or download the .po files and work with your favorite localization tool. We use translation memory, terminology file, and you can add as many comments as you want to help you or your fellow to get add context to your files. Each string has a unique reference that is reflected in the UI with a special tagged version. And if you have no clue of what the string means, just ask, we share the same doubts!
If you are still dealing with .sdf files, please check your file using gsicheck (or if as me you're doing localization not always in a very recommended way), you will save a fair amount of Andras time and provide him with clean files. See how to do so here: http://wiki.documentfoundation.org/TipsTricksl10n.

On Pootle, you'll see other projects, like website or ask.libreoffice. If you have enough resources to localize these projects, that will ease the access of your users to get support and information in their language if you provide a translated website, see here for more information: http://wiki.documentfoundation.org/Translating_LibreOffice.

And now, you know what? I've a very good news for you: you're just in time to localize the LibreOffice 4.0 version :-)