I mean it doesn’t crash or something it’s just it doesn’t change the currency position.

Example:
For US Dollars have to be $10,00
But for Euro in Spain we use 10,00€
There is an easy way to change the currency position in the Locale (lenguage) you want.
In my case I wanted to change the € simbol for the Spanish locale on my Magento installation.

1. Go from your root folder to /lib/Zend/Locale/Data

2. Find the lenguage file. In my case es.xml

3. Look for <currencyFormat>

A line just below you will find the <pattern>
Change the side of the weird simbol and leave it like this:

Before

After

Now this becomes interesting. Try to refresh the Magento Cache and the browser cache. In my case nothing happened. The change made effect itself an hour after this.
I’m not sure but I think its something about caching those XML files.
Anyway, just be patient until the change comes by itself.