You can add your language file to the "lang" folder inside resources folder. After that just go to Settings page after login to your Admin account and change language.
For example:- To translate to French you just need to translate the "english.php" file from "resources/lang" folder and save it as "french.php" inside "resources/lang" folder. Now you can change the default language for web app to French by changing the language in Settings after login to your Admin account.
If you want to remove the english file and don't want users to switch to other languages then make sure you have only your language file in "resources/lang" folder and change the PRIMARY_LANGUAGE constant in "resources/lang.php" file to your language file name. For example, If I want users to use app only in French language and my language file name is french.php then I have to change the constant in "resources/lang.php" as shown below.
