load_plugin_textdomain()
Function: Loads a plugin’s translated strings.
Source: wp-includes/l10n.php:915
load_muplugin_textdomain()
Function: Loads the translated strings for a plugin residing in the mu-plugins directory.
Source: wp-includes/l10n.php:963
load_theme_textdomain()
Function: Loads the theme’s translated strings.
Source: wp-includes/l10n.php:1002