The true-false question type intentionally works the way it does.
It was implemented a long time ago, before the multilang filter existed. So at the time, it made sense for the words true and false in the question to be stored in the language of the teacher who created the question, because presumably that was the same language as the question text.
Now, of course, the situation has changed, and we probably need a better solution. However, it is not immediately clear to me what the right solution is. For teachers who don't bother with the multilang filter, the old behaviour is better. And what if a teacher sets up a question with the questiontext available in English and French, and then a German student comes along. Which language should they see the words true and false in?
So before anything else can be done, someone needs to sit down a work out what the correct behaviour is in all situations (a page attached to http://docs.moodle.org/en/Developer_notes would be a good place to do that).
As a work-around, you can always use a multiple-choice question with two choices.
Improvement
The true-false question type intentionally works the way it does.
It was implemented a long time ago, before the multilang filter existed. So at the time, it made sense for the words true and false in the question to be stored in the language of the teacher who created the question, because presumably that was the same language as the question text.
Now, of course, the situation has changed, and we probably need a better solution. However, it is not immediately clear to me what the right solution is. For teachers who don't bother with the multilang filter, the old behaviour is better. And what if a teacher sets up a question with the questiontext available in English and French, and then a German student comes along. Which language should they see the words true and false in?
So before anything else can be done, someone needs to sit down a work out what the correct behaviour is in all situations (a page attached to http://docs.moodle.org/en/Developer_notes would be a good place to do that).
As a work-around, you can always use a multiple-choice question with two choices.