Answering the second question first: `display_name` calls `model_name` which is already locale-aware. So with no locale set, `Investigation.display_name` should return `"Investigation"`, but with a locale definition like this:

    'en-NEXTGEN':
      activerecord:
        models:
          Investigation: Sequence

then `Investigation.display_name` will return `"Sequence"`. Put another way, `t(class)` and `class.model_name` are functionally equivalent. So we don't need to deprecate the use of `display_name` (in fact, I just added a few uses to the PR.)

To answer the first question, calling the `human` method on the ActiveModel::Name object returned by `model_name` returns a demodulized string, so we are stripping the module name. (`human` seems to manage what we were doing with `demodulize.underscore.humanize`.)