Add German translations and fix Credo warnings

Add translations for 'Current Cycle Payment Status' and 'Last Cycle
Payment Status'. Replace length/1 with Enum.empty?/1 in seeds tests
to fix Credo warnings.

test/seeds_test.exs

@@ -56,7 +56,7 @@ defmodule Mv.SeedsTest do
       members_without_fee_type =
         Enum.filter(members, fn member -> member.membership_fee_type_id == nil end)
 
-      assert length(members_without_fee_type) > 0,
+      assert not Enum.empty?(members_without_fee_type),
              "At least one member should have no membership fee type assigned"
     end
 
@@ -78,7 +78,7 @@ defmodule Mv.SeedsTest do
       Enum.each(fee_types, fn fee_type ->
         members_for_type = Map.get(members_by_fee_type, fee_type.id, [])
 
-        assert length(members_for_type) > 0,
+        assert not Enum.empty?(members_for_type),
                "Membership fee type #{fee_type.name} should have at least one member assigned"
       end)
     end
@@ -95,7 +95,7 @@ defmodule Mv.SeedsTest do
         |> Enum.filter(&(&1.membership_fee_type_id != nil))
 
       # At least one member should have cycles
-      assert length(members_with_fee_types) > 0,
+      assert not Enum.empty?(members_with_fee_types),
              "At least one member should have a membership fee type"
 
       # Check that cycles exist and have various statuses