I was thinking for multiple language support the Laravel Framework in PHP will be very useful to boost the Site and App Performance.
If you want Responsive Site Then only Bootstrap is Fine but for Mobile App development I think API development in Laravel will be useful.
We have just Completed Two Projects on Freelancer with The Requirement For Designing the Responsive Website in CSS Bootstrap 3 Framework and they seem to like our Work. Hope you Like it too just Give Us a Try.
We have excellent, committed team of experienced resources with expertise in PHP and Android Application development. Team has worked on HTML5, CSS3, Java Script, Angular.js, JQuery, REST APIs, Laravel PHP framework, Webservices for many years. We are available to work on your project and achieve success in project delivery.