Add gettext to rdfd.io build

Author: codingjoe

.readthedocs.yaml

@@ -6,11 +6,13 @@ build:
   os: ubuntu-24.04
   tools:
     python: "3"
-mkdocs:
-  configuration: mkdocs.yml
+  apt_packages:
+    - gettext
 python:
   install:
     - method: pip
       path: .
       extra_requirements:
         - docs
+mkdocs:
+  configuration: mkdocs.yml