Update :placeholders share example

- previously, we mistakenly assumed that in languages which do not use
plurals, the translation would always contain placeholders matching
the English singular form
- for languages, which do not use plurals, we'll be watching for
mistakenly added plural forms

spec/shared/i18n/placeholders.rb

@@ -1,22 +1,35 @@
 shared_examples :placeholders do |dir|
   it "translations preserve placeholders in strings" do
     errors = {}
+    false_negatives = {}
+    incorrect_plurals = []
 
     Pathname.glob(File.join(dir, "**", "*.po")).each do |po_file|
       po = FastGettext::PoFile.new(po_file)
       locale = po_file.dirname.basename.to_s
+      false_negatives[po_file.to_s] = []
       next if locale == 'en' # There's no need to test english .po
+
       po.data.each do |original, translation|
-        next if translation.nil?
-        # Chinese translations do not have plural forms
-        original = original.split("\u0000").first if locale == 'zh_CN' && original.present?
-        placeholders = original.scan(/%{\w+}/)
-        placeholders.sort!
-        next if placeholders.empty?
-        translated_placeholders = translation.scan(/%{\w+}/)
-        translated_placeholders.sort!
-        if placeholders.uniq != translated_placeholders.uniq
-          errors.store_path(po_file.to_s, original, translation)
+        next if translation.nil? || !original.include?("%{") # Skip if string is not translated or original does not contain %{}
+
+        if %w[ja zh_CN].include?(locale) && original.include?("\u0000") # Chinese and Japanese translations do not have plural forms
+          if translation.include?("\u0000") # there should be only one translated form
+            incorrect_plurals << translation
+            next
+          end
+          singular, plural = original.split("\u0000").map { |str| str.scan(/%{\w+}/).sort.uniq }
+          translated_placeholders = translation.scan(/%{\w+}/).sort!.uniq
+          if singular != translated_placeholders && plural != translated_placeholders
+            errors.store_path(po_file.to_s, original, translation)
+          end
+          false_negatives[po_file.to_s].append(original.split("\u0000").first)
+        else
+          origin = original.scan(/%{\w+}/).sort.uniq
+          transl = translation.scan(/%{\w+}/).sort.uniq
+          if origin != transl && !false_negatives[po_file.to_s].include?(original)
+            errors.store_path(po_file.to_s, original, translation)
+          end
         end
       end
     end
@@ -31,13 +44,15 @@
       end
     end
     expect(errors).to be_empty
+    expect(incorrect_plurals).to be_empty
   end
 
   it "gettext strings do not contain interpolations" do
     errors = []
     Pathname.glob(File.join(dir, "**", "*.pot")).each do |pot_file|
       File.open(pot_file).each do |line|
         next unless line =~ /^.*(".*\#\{[.\w]+\}.*")$/
+
         errors.push($1)
       end
     end