This "Do we have any languages to validate this? " you can find in /Sources/Load.php (if use notepad++ editor find line 528)
This "And where should I put db_settings.php ?" ...not necessary (everything is automatic) when you install your mod, read this "This file should be able to execute standalone."
For css/index.css just add at the end
/***************************************
START LANGUAGE MENU STYLES
***************************************/
/*The main language button menu container*/
#language_menu {
position: relative;
display: inline;
float: right;
padding: 10px;
}
/*Make the buttons align horizontaly*/
#language_menu form {
padding: 0;
display: inline;
}
/* Pointer to easly identify "clickable" buttons */
#language_menu form button {
font-size:10px;
cursor: pointer;
}
/* Default cursor and different color for distinction of current language */
#language_menu form button.active {
color: #666;
cursor: default;
}
#language_menu img.langicon {
padding-right: 4px;
float: left;
margin-top: 2px;
}
#language_menu button.langflagbutton {
background: none;
border:none;
padding: 0;
margin:0;
opacity: 0.5;
}
#language_menu button.langflagbutton:hover {
opacity: 1;
}
#language_menu button.langflagbuttonactive {
background: none;
border:none;
padding: 0;
margin:0;
cursor: default;
opacity: 1;
}
/***************************************
END LANGUAGE MENU STYLES
***************************************/