When installing Joomla, the installer script asked you to select a language. English language was selected by default. But you remember well, you selected your native language. However, when you opened Joomla backend, everything is still in English.
Joomla installer script offers you to select many languages, but core Joomla comes only in English. This doesn't mean that you (or your clients) must use the English version of Joomla. You just need one more step to enable Joomla to "speak" your language. Joomla language installation is similar as installation of any other extension (component, module, plugin or template).
The first step is to find correct language file. The best address where you should start your serch is extensions.joomla.org. If someone from your country translated Joomla, those files are most likely published on this site. When you open Joomla Extensions site, go to the Languages section and look for Translations category there. Over 50 language packs are currently available. Download the right pack for your language and make sure that you downloaded the correct version. Not all translations are available for all versions of Joomla.
Some Joomla translators offered full Joomla installation with language pre-installed. However, if you are about to install our template using HotStart method, you can't use such Joomla installations because each HotStart installation is a new Joomla installation. Therefore, make sure you downloaded only Joomla language pack, not full Joomla installation in your language.
Once you have the translation pack for your language, in Joomla backend go to Extensions Manager > Install. Choose the file you downloaded and install it. If you get error (such as "XML file not available..."), you probably use translation that's not made for your version of Joomla. If you get message about successful installation, you can proceed to the activation of new language pack.
Go to Extensions > Language Manager. You should see your new installed language in the list. English language is still set as default, so it's time to change that now. Select your language and click Default icon (top right corner). Instantly, Joomla backend panel are in your language. The same transformation is visible in the frontend of your site. All Joomla specific language strings (such as "Read more") are translated to your language.
Last but not least, if there's no language pack available for your language, and you badly need it, maybe you can make it yourself and then share it with Joomla community. Look for folder /languages/en-GB on the computer or hosting space where you installed Joomla. There are many textual files with INI extension. If you know English, you can make version of those files in your language.
Format of those INI files is:
You should translate "Some words" from English to your language. However, you mentioned there are hundreds of text lines. That gives you an idea that translation process could take a long time.