Now every such string MUST be encapsulated into ?T() macro.
The macro itself is defined in include/translate.hrl.
Example:
-module(foo).
-export([bar/1]).
-include("translate.hrl").
bar(Lang) ->
translate:translate(Lang, ?T("baz")).
Note that support for older specification is completely dropped,
i.e. no backward compatibility is provided since the XEPs are
still very experimental and being changed drastically
Evgeny Khramtsov