refactor: change meta class structure to include types.

Introduce requiredness of translations via implemented interface.

src/core/things/Catalog.ts

@@ -13,8 +13,13 @@
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
 import {SCAcademicTermWithoutReferences} from '../base/AcademicTerm';
-import {SCThingWithCategoriesSpecificValues, SCThingWithCategoriesWithoutReferences} from '../base/ThingWithCategories';
+import {
+  SCThingWithCategoriesSpecificValues,
+  SCThingWithCategoriesWithoutReferences,
+  SCThingWithCategoriesWithoutReferencesMeta,
+} from '../base/ThingWithCategories';
 import {SCThingMeta, SCThingType} from '../Thing';
+import {SCMetaTranslations} from '../types/i18n';
 
 /**
  * A catalog without references
@@ -62,10 +67,39 @@ export interface SCCatalog extends SCCatalogWithoutReferences {
   type: SCThingType.Catalog;
 }
 
-/**
- * Catalog meta data
- */
-export class SCCatalogMeta extends SCThingMeta {
+  /**
+   * Catalog meta data
+   */
+export class SCCatalogMeta extends SCThingMeta implements SCMetaTranslations<SCCatalog> {
+  /**
+   * Translations of fields
+   */
+  fieldTranslations = {
+    de: {
+      ... SCThingWithCategoriesWithoutReferencesMeta.getInstance<SCCatalogCategories,
+            SCThingWithCategoriesSpecificValues>().fieldTranslations.de,
+    },
+    en: {
+      ... SCThingWithCategoriesWithoutReferencesMeta.getInstance<SCCatalogCategories,
+            SCThingWithCategoriesSpecificValues>().fieldTranslations.en,
+    },
+  };
+
+  /**
+   * Translations of values of fields
+   */
+  fieldValueTranslations  = {
+    de: {
+      ... SCThingWithCategoriesWithoutReferencesMeta.getInstance<SCCatalogCategories,
+            SCThingWithCategoriesSpecificValues>().fieldValueTranslations.de,
+      type: 'Verzeichnis',
+    },
+    en: {
+      ... SCThingWithCategoriesWithoutReferencesMeta.getInstance<SCCatalogCategories,
+            SCThingWithCategoriesSpecificValues>().fieldValueTranslations.en,
+      type: SCThingType.Catalog,
+    },
+  };
 }
 
 /**