Fix invalid language resulting in no fallback being set on statuses (#17722)

app/helpers/languages_helper.rb

@@ -241,6 +241,15 @@ module LanguagesHelper
     code
   end
 
+  def valid_locale_cascade(*arr)
+    arr.each do |str|
+      locale = valid_locale_or_nil(str)
+      return locale if locale.present?
+    end
+
+    nil
+  end
+
   def valid_locale?(locale)
     locale.present? && SUPPORTED_LOCALES.key?(locale.to_sym)
   end

app/services/post_status_service.rb

@@ -162,7 +162,7 @@ class PostStatusService < BaseService
       sensitive: @sensitive,
       spoiler_text: @options[:spoiler_text] || '',
       visibility: @visibility,
-      language: valid_locale_or_nil(@options[:language].presence || @account.user&.preferred_posting_language || I18n.default_locale),
+      language: valid_locale_cascade(@options[:language], @account.user&.preferred_posting_language, I18n.default_locale),
       application: @options[:application],
       rate_limit: @options[:with_rate_limit],
     }.compact

app/services/update_status_service.rb

@@ -94,7 +94,7 @@ class UpdateStatusService < BaseService
     @status.text         = @options[:text].presence || @options.delete(:spoiler_text) || '' if @options.key?(:text)
     @status.spoiler_text = @options[:spoiler_text] || '' if @options.key?(:spoiler_text)
     @status.sensitive    = @options[:sensitive] || @options[:spoiler_text].present? if @options.key?(:sensitive) || @options.key?(:spoiler_text)
-    @status.language     = valid_locale_or_nil(@options[:language] || @status.language || @status.account.user&.preferred_posting_language || I18n.default_locale)
+    @status.language     = valid_locale_cascade(@options[:language], @status.language, @status.account.user&.preferred_posting_language, I18n.default_locale)
     @status.edited_at    = Time.now.utc
 
     @status.save!