i18n: Use argument for track count on splash screen.

Fixes a bug reported by Albert Astals Cid on behalf of the translation
team. Also has the effect on my system of inserting thousands separators
like normal, perhaps I should have made this switch earlier...

Albert, please let me know if the translators desire this to be
backported, as it stands now I have no intention on breaking i18n freeze
for 4.10.


FIXED-IN:4.11