Fix in testsuite.

test/proposal_runner_test.rb

@@ -60,6 +60,8 @@ class C < ::Installation::ProposalStore; end
         .with("keyboard_proposal", ["Description", {}]).and_return(keyboard_description)
       allow(Yast::WFM).to receive(:CallFunction)
         .with("hwinfo_proposal", ["Description", {}]).and_return(hwinfo_description)
+      # Language class is missing in buildroot -> mock it
+      allow(Yast::Language).to receive(:language).and_return("en_US")
     end
 
     it "do nothing if run non-interactive" do
@@ -171,7 +173,6 @@ class C < ::Installation::ProposalStore; end
             .and_call_original
 
           # we need ProposalStore#make_proposal to call the callback
-          # for some reason mocking using expect do not work in this case
           allow(Yast::WFM)
             .to receive(:CallFunction)
             .and_return(