The current code is available at https://github.com/omeka/Omeka, we're not using our old SVN (or that i18n branch) anymore.
The correct version that supports translations is called 1.5-dev, and is the "master" branch on GitHub.
You can use the Omeka GitHub repository similarly to SVN (only using Git, of course), or you can also get GitHub to generate a zip for you to download by clicking the "ZIP" button.
In any case, to test a translation on 1.5-dev, you place the .mo file in the application/languages folder, then set the "locale" setting in config.ini to the part before ".mo."
Apologies if this all sounds a little confusing at this stage. We'll also make an easier-to-use pre-release zipped copy of 1.5 for people to test with, so you might want to wait for that option instead. For this zipped version, we'll include all the necessary files for any translations that have been submitted on Transifex, and all you'll have to do is set the "locale" setting for your desired language.