Add family vocabulary exercises in Bisaya course content

- Introduced a new set of multiple choice and gap fill exercises focused on family-related vocabulary in Bisaya, enhancing language learning.
- Included detailed explanations for each term to provide context and aid understanding for learners.
- Removed dummy exercises for unknown lessons, streamlining the exercise return logic for better user experience.

frontend/src/components/AppNavigation.vue

@@ -29,7 +29,7 @@
             >&nbsp;</span>
             <span>{{ subitem?.label || $t(`navigation.m-${key}.${subkey}`) }}</span>
             <span
-              v-if="subkey === 'forum' || subitem.children"
+              v-if="subkey === 'forum' || subkey === 'vocabtrainer' || subitem.children"
               class="subsubmenu"
             >&#x25B6;</span>
 
@@ -47,7 +47,26 @@
               </li>
             </ul>
 
-            <!-- Weiteres Untermenü Ebene 2 -->
+            <!-- Vokabeltrainer-Unterliste (Sprachen) -->
+            <ul
+              v-else-if="subkey === 'vocabtrainer' && vocabLanguagesList.length"
+              class="submenu2"
+            >
+              <li
+                @click="handleItem({ path: '/socialnetwork/vocab/new' }, $event)"
+              >
+                {{ $t('navigation.m-sprachenlernen.m-vocabtrainer.newLanguage') }}
+              </li>
+              <li
+                v-for="lang in vocabLanguagesList"
+                :key="lang.id"
+                @click="handleItem({ path: `/socialnetwork/vocab/${lang.id}` }, $event)"
+              >
+                {{ lang.name }}
+              </li>
+            </ul>
+
+            <!-- Weiteres Untermenü Ebene 2 -->
             <ul
               v-else-if="subitem.children"
               class="submenu2"
@@ -126,7 +145,8 @@ export default {
   data() {
     return {
       forumList: [],
-      friendsList: []
+      friendsList: [],
+      vocabLanguagesList: []
     };
   },
   computed: {
@@ -149,6 +169,7 @@ export default {
       this.loadMenu();
       this.fetchForums();
       this.fetchFriends();
+      this.fetchVocabLanguages();
     }
   },
   beforeUnmount() {
@@ -196,6 +217,16 @@ export default {
       }
     },
 
+    async fetchVocabLanguages() {
+      try {
+        const res = await apiClient.get('/api/vocab/languages');
+        this.vocabLanguagesList = res.data?.languages || [];
+      } catch (err) {
+        console.error('Error fetching vocab languages:', err);
+        this.vocabLanguagesList = [];
+      }
+    },
+
     openForum(forumId) {
       this.$router.push({ name: 'Forum', params: { id: forumId } });
     },