How to install a new language in Joomla 1.5
First of all, you should download the language pack which you wish to install. You can find a lot of language packs at this URL.
Once you have downloaded the language pack, you can install it from your Joomla 1.5 admin area > Extensions > Install/Uninstall.
Then you can set the newly-installed language as your Joomla's default from Extensions > Language Manager. Once there, simply check the box next to it and then click the Default button located at the top-right Joomla menu.
If you have problems installing a new language in Joomla 1.5, ask your host for assistance. SiteGround provides the best Joomla hosting and such requests are handled with ease.
Joomla is a powerful software that is easy to work with once you have the right host to support you. Before you lose any more time with the wrong host, check out the SiteGround Joomla hosting offer.