This blog I most will record my learning bluemix experience,I hope my blog will also improve your skills about BlueMix.
If you can't find a starter in the IBM® Bluemix™ catalog
that provides the runtime that you want, you can bring an existing
buildpack to Bluemix. You can specify a custom, Cloud Foundry-compatible buildpack when
you deploy your application by using the cf push command.
For Bluemix side ,you can use cf buildpackes command to list all buildpacks they suupported.
If you want to use custmize buildpack for Bluemix, there are several articles you can reference that.I list some links for your reference.So you may use go,php,python,Nginx buildpack to write your application.
Use a custom Go buildpack with IBM Bluemix
Diving Into PHP and BlueMix
Create a static web site on IBM Bluemix