Here are some notes I have from my limited experience working to test application UI in both LTR and RTL.  Please drop a comment if you have better experiences, I’d love to be able to save a bit of time.

GNOME RTL

In the GNOME world to do a simple test of an RTL language you could start up the application with the LANG environment variable set to an appropriate language.  For instance:

LANG=he_IL eog

Thunderbird RTL

With Thunderbird I’ve found a number of options to make this happen.

The UILocale flag can be added your command arguments.

thunderbird -UILocale he

However Thunderbird, as compiled from hg, or download nightly likely doesn’t contain the translations needed to run that test successfully.

For the nightly build you’ll want to grab a translation XPI from the comm-central-l10n nightly builds.  You can drag any of those XPI links into the Thunderbird add-on manager window to install them.  (saves a bit of time compared to downloading and installing)

For your compiled builds the process seems a bit longer and more difficult getting the translations from l10n-central built in.  I gave up half way through as there is an easy method out there already, at least for simple testing.

Force RTL Extension

An easy alternative approach is to use the Force RTL extension, which I only just found out about today.  The extension provides an option in the tools menu to trigger RTL mode, which is really a lot better than trying a language you don’t understand.  If all you need is to test layout in an RTL this works really well.

For a long time Thunderbird has been using the same theme for Linux and Windows, resulting in an ugly and out of place Linux theme.  However now Magnus has a patch is up to create a gnomestripe theme space.  Magnus already moved Thunderbird menus over to using the gtk stock icons.

Here’s a screenshot (courtesy of Michael Monreal) of Thunderbird using the desktop icon spec.

Now we can start the move over to using the Tango icon set!