Hi,
I found this bug, and it is very easy to reproduce:
1 - Install NOP 1.8 in a new database (I do the installation from vstudio development server, not an IIS virtual directory)
2 - Download Spanish language extension (https://www.nopcommerce.com/p/158/spanish-language-pack.aspx)
3 - Uncompress the file, we got an XML
4 - Login in NOP as administrator, go to Configuration -> Location -> Languages
5 - Click "Add new"
6 - Fill the form with this data:
Name: Espanol
Culture: es-ES (international)
Flag image file: es.png
Published: checked
Display order: 2
7 - Click "save"
8 - Import XML appears, choose the spanish xml file and click "Import"
9 - Import takes some time, but there are not visible errors or exceptions
10 - Click save. If you do so... I think it behaves like no XML file was imported (you see resource keys in labels, instead of its values)
I've discovered (after some reinstallations), that if I do not click at the "save" button it works...