More fixes, translated remaining string

As indicated by AaronVanGeffen.

I quickly walked trough the entire file, fixing some translations, including a few for consistency, and a few to prevent overflowing. Also translated what _seemed_ like the only remaining untranslated string! (Not counting strings that are currently untranslatable.) In other words, it means dutch.txt is as complete as it can currently get.

@AaronVanGeffen: could you take a look as well and tell if you can find any errors?