Fix the cleanup prompt language and harden detection parsing

Review found the detected language was only switching the glossary rule, not
the base prompt: a detected Turkish recording with an English interface got the
English cleanup prompt with a Turkish glossary footnote. Both now follow the
spoken language, and the detected-language value is guarded against a server
that returns something other than a string. The record reply is covered by a
CLI test.

tests/test_cli.py

@@ -722,6 +722,13 @@ class Replies(DikteTest):
         self.assertEqual(code, 0)
         self.assertEqual(out.strip(), "Book it for Thursday.")
 
+    def test_the_json_answer_carries_the_detected_language(self):
+        code, out, _ = self.run_verb(
+            ["--json", "record"],
+            {"ok": True, "text": "Selam", "speech_language": "tr"})
+        self.assertEqual(code, 0)
+        self.assertEqual(json.loads(out)["speech_language"], "tr")
+
     def test_a_dictation_that_failed(self):
         code, out, err = self.run_verb(["stop", "--wait"],
                                        {"ok": False, "error": "No speech detected"})