String encapsulation for improved translation

The idea of a template system for translation is cool. 
In case the string "page {current page} of {total pages}" is translated to "第{当前页码}页，共{总页码}页" in Chinese, we need the template engine like this:
self.page_info_text.text = util.template{ 
    _("page {current page} of {total pages}"),
    [_("current page" )] = self.page,
    [_("total pages")] = self.page_num
}
so that even the translators translate the placeholders in the braces the result strings are also valid. And we may need to add an note on the tutorial of the template system that the braces around the placeholder should be half width "{}" instead of full width "｛｝" especially for CJK languages in which sometimes it's strange to mix full width characters with half width characters, and we should emphasize on it.