Use new intllib format strings

locale/de.txt

@@ -1 +1 @@
-%d/%d = %d/%d
+@1/@2 = @1/@2

locale/template.txt

@@ -1,4 +1,3 @@
-# Shows number of occupied (first number) vs number of total inventory slots (second number).
-# “%d” is a placeholder which stands for a number.
+# Shows number of occupied (@1) vs number of total inventory slots (@2).
 # Try to keep the translation short.
-%d/%d =
+@1/@2 =