Fix s3proxy language toggle with centraldashboard button

[mathis-marcotte]

We added a new language toggle button in central dashboard (https://github.com/StatCan/kubeflow/issues/171)

This toggle doesn't work with the s3proxy instance because of the way that it handles it's internationalization.

We should look into how s3proxy is getting translated so that it shares the same language as the rest of the app when it gets displayed.

Some examples of how we could do this would be to either have the language in the url like for jupyter-apis or to have the language in the request call to load s3 proxy.