Add `language` stanza to cask DSL.

Library/Homebrew/cask/lib/hbc/dsl.rb

@@ -64,6 +64,7 @@ module Hbc
                             :depends_on,
                             :gpg,
                             :homepage,
+                            :language,
                             :license,
                             :name,
                             :sha256,
@@ -98,6 +99,31 @@ module Hbc
       @homepage ||= homepage
     end
 
+    def language(*args, &block)
+      @language ||= {}
+
+      if !args.empty? && block_given?
+        args.each do |arg|
+          MacOS.languages.each_with_index do |l, index|
+            string_or_regex = arg == :default ? %r{^en} : arg
+            next unless l.match(string_or_regex)
+            next unless @language[:level].nil? || @language[:level] > index
+            @language = {
+                          block: block,
+                          level: index,
+                        }
+          end
+        end
+
+        if args.include?(:default)
+          # :default has to be the last language block in order to assign return value of the selected `language` block to `@language`
+          @language = @language[:block].call
+        end
+      else
+        @language
+      end
+    end
+
     def url(*args, &block)
       url_given = !args.empty? || block_given?
       return @url unless url_given

Library/Homebrew/cask/lib/hbc/dsl/base.rb

@@ -8,7 +8,7 @@ module Hbc
         @command = command
       end
 
-      def_delegators :@cask, :token, :version, :caskroom_path, :staged_path, :appdir
+      def_delegators :@cask, :token, :version, :caskroom_path, :staged_path, :appdir, :language
 
       def system_command(executable, options = {})
         @command.run!(executable, options)