If you can't find the application listed on Transifex, this is roughly how you can do a new translation from the source package (in case the application is already "prepared" for translations, i.e. "gettextized"). Please be sure to contact the application maintainer first, as (s)he will be able to tell you exactly how translations are handled for that specific project. Sometimes it makes more sense to use the development repository (SVN, Git, etc..) instead of the source package, for example. In other cases, maybe the app has already been translated into your language, but the new translations have not been released yet.

Here's a quick HOW-TO for packages in Maemo.org Extras:

• Go to http://maemo.org/packages/
• Search for the package you want to translate
• Click on the search result
• Select the "Fremantle Extras-Devel free armel" package
• Click on the link for "Source:"
• Download the .tar.gz file
• Extract the downloaded file and look for a messages.pot file
• If you find the messages.pot file, rename it to yourlang.po (e.g. de.po for german) - alternatively, use an existing .po file and copy it to yourlang.po
• Open the .po file with tools like poedit, translate and then send it to the maintainer (the maintainer can be found on the maemo.org/packages page as well)

It depends on the license of the application - sometimes you have to share the source if you distribute the binary. What you need to do is set up some kind of build environment (Scratchbox) and build the package with your added translation from source and install that on your device (that's the recommended way - it would work if you compile the .po file to a .mo file [poedit does this automatically] and copy it to the right folder on the device, but that's really awkward and something you don't really want to do).

In short: The easiest (and most sane) way to do this is to submit the translated .po file to the application author and wait for an updated package.