[TYPO3-english] Change language of login screen

[Bernhard Schenkenfelder]

I created two websites for NGOs in Bolivia and was able to change both the frontend and the backend language to Spanish. However, I would also like to change the login screen language to Spanish:

http://www.musol.org.bo/typo3/index.php
http://www.complejosolar.com/typo3/index.php

Many thanks for your help!

Bernhard