I use as example the german translation file. Dont forget to use it also for the plugins.
Checkout the svn version
Updating translation files
run in mythtv directory
Translate file in the directory: i18n eg: i18n/mythfrontend_de.ts
You can use any editor for this, or linguist from qt.
svn diff i18n/mythfrontend_de.ts >translation.diff
Submit the Patch
Submit the Diff to Oscar, via the URL: http://svn.mythtv.org/trac/newticket
Summary: [PATCH i18n] german translation