Leave at the default value UTF-8 unless your language contains characters not supported by this charset. If you do change it, files need to be resaved under that charset. To do that, open the language file you use from the lang folder in Notepad and then go to File > Save As and choose Encoding Type "ANSI". Save and then reupload and it should be fine again.
Choose how the date will be displayed throughout your admin area.
Client Date Format
Choose how the date will be displayed throughout your client area.
The default option in the country dropdown on the registration and checkout pages.
The language that all visitors will see your WHMCS installation in.
Enable Language Menu
A dropdown menu will appear allowing visitors to choose the language of your installation. Unticking this option does not prevent the language from being changed by specifying the language variable in the address bar.
You can translate into your own language by copying one of the existing text files in the /lang folder and renaming it. For more information refer to this page.
Dynamic Field Translations
Dynamic Field Translation allows you to localise supported database field values into multiple languages. For example this enables clients who use your client area and shopping cart in English to see a product name as Silver whilst French customers would see it as Argent.
Once enabled here, a Translate button will appear next to translatable fields. More information is available here.
Remove Extended UTF-8 Characters
This setting is on by default which is the recommended state. Only disable this setting if you're using the utf8mb4 MySQL connection charset and utf8mb4_unicode_ci table collation. Disabling this option with another charset and collation will result in problems when 4-byte UTF characters are used in support tickets (eg. Emoji icons or some Kanji characters).
UNtick this option to remove the country flag and automated country code prefix selection on the phone number fields through the client and admin area. More Information.