Just to note, in this case, if you are not changing any of the PHP code that calls this language string, then it is highly unlikely that {$a->number} or {$a->name} will be filled in.
When the lang string is used in Moodle (by calling get_string()) the values to use need to be passed in at the same time. At the moment just a single number is passed in - you are wanting an object with 2 values in it, which is not being provided.