Tested this solution a bit more (modified from this post) try this (replace “Travel” with your category name):
<script>
Discourse.ExternalNavItem = Discourse.NavItem.extend({
href : function() {
return this.get('href');
}.property('href')
});
I18n.translations.en.js.filters.bugs = { title: "Bugs", help: "Open Bugs" };
I18n.translations.en.js.filters.google = { title: "Google", help: "Navigate to Google" };
Discourse.NavItem.reopenClass({
buildList : function(category, args) {
var list = this._super(category, args);
if(category && category.name == "Travel") {
list.push(Discourse.ExternalNavItem.create({href: '/category/bug', name: 'bugs'}));
list.push(Discourse.ExternalNavItem.create({href: 'https://google.com', name: 'google'}));
}
return list;
}
});
</script>