Replace i18n view spec with helper spec (mastodon#24966)

spec/locales/i18n_spec.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'I18n' do
+  describe 'Pluralizing locale translations' do
+    subject { I18n.t('generic.validation_errors', count: 1) }
+
+    context 'with the `en` locale which has `one` and `other` plural values' do
+      around do |example|
+        I18n.with_locale(:en) do
+          example.run
+        end
+      end
+
+      it 'translates to `en` correctly and without error' do
+        expect { subject }.to_not raise_error
+        expect(subject).to match(/the error below/)
+      end
+    end
+
+    context 'with the `my` locale which has only `other` plural value' do
+      around do |example|
+        I18n.with_locale(:my) do
+          example.run
+        end
+      end
+
+      it 'translates to `my` correctly and without error' do
+        expect { subject }.to_not raise_error
+        expect(subject).to match(/1/)
+      end
+    end
+  end
+end