Consistency for t2() parameters

For the singular version we have %3$d but for the plural version we have %3$s. Let's use %3$s.

As a general rule (if we don't have any special formatting needs), I think we should always use %s instead of others type specifiers. This way we'll have a greater flexibility (eg formatting numbers with comma vs dot for decimal separators, and so on...) without having to change the translatable string.