When changing the source language, the html-tools UI will often show a bunch of greyed out buttons, and the user has to fish for possible languages in the right-hand side drop-down. This is confusing (user might think "are there no languages to translate into?") and annoying. A simple solution is to reorder the list so that all possible target languages are shown first, then the list of greyed-out languages. See ticket 25 for details and progress tracking.
For further information and guidance on this task, you are encouraged to come to our IRC channel.