By Default, the application are loaded with flags of all majors countries. Therefore just Open aplication/layouts/scripts/carcms/blocks/change_lang.phtml page please add the following code
Language codes follow the convention of a two letter lowercase language name, followed by an underscore, followed by two upper-case latters signifying the country code which follows i18n localization standard. According the codes above, Here in the
rel attribute of tag a 'xx_XX' is the language code that you put in application/modules/Settings/forms/en_US.GlobalSettingsForm.ini.
Please open application/modules/Settings/forms/source/en_US.GlobalSettingsForm.ini file and find below line :
settings.elements.default_language.options.multiOptions.fr_FR = "French" and add an new line to include your language as follows :
Example : settings.elements.default_language.options.multiOptions.xx_XX = "My new XX Language" and finally save it.
The Country based flag images are located at images/adminImages/flagsImage/ directory in .gif extension. Choose your flag and pick the correct image file to display it accordingly. Please see the screen shots shown below.