feat(models): add LanguageMixin to Work, Expression

Add select field for language to Work, Expression
entities via new LanguageMixin. TextChoices use
ISO 639-3 codes for values, German verbose names
for labels (+ 2-letter codes for variable names).

apis_ontology/migrations/0047_expression_language_work_language.py

@@ -0,0 +1,42 @@
+# Generated by Django 4.2.11 on 2024-03-28 12:13
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("apis_ontology", "0046_expression_isbn"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="expression",
+            name="language",
+            field=models.CharField(
+                blank=True,
+                choices=[
+                    ("deu", "Deutsch"),
+                    ("eng", "Englisch"),
+                    ("fra", "Französisch"),
+                ],
+                default="",
+                max_length=3,
+                verbose_name="Sprache",
+            ),
+        ),
+        migrations.AddField(
+            model_name="work",
+            name="language",
+            field=models.CharField(
+                blank=True,
+                choices=[
+                    ("deu", "Deutsch"),
+                    ("eng", "Englisch"),
+                    ("fra", "Französisch"),
+                ],
+                default="",
+                max_length=3,
+                verbose_name="Sprache",
+            ),
+        ),
+    ]

apis_ontology/models.py

@@ -288,7 +288,7 @@ class Meta:
 
 
 @reversion.register(follow=["rootobject_ptr"])
-class Work(TitlesMixin, StatusMixin, AbstractEntity):
+class Work(TitlesMixin, LanguageMixin, StatusMixin, AbstractEntity):
     """
     The abstract notion of an intellectual creation, irrespective
     of its exact transmitted version, language or other form.
@@ -535,7 +535,12 @@ class Meta:
 
 @reversion.register(follow=["rootobject_ptr"])
 class Expression(
-    TitlesMixin, DescriptionMixin, NotesMixin, StatusMixin, AbstractEntity
+    TitlesMixin,
+    DescriptionMixin,
+    LanguageMixin,
+    NotesMixin,
+    StatusMixin,
+    AbstractEntity,
 ):
     """
     A concrete representation of a given Work,