Do not hardcode locale unless certainly necessary (#6791)

Merge pull request 6791

lib/jekyll.rb

@@ -35,7 +35,6 @@ require "colorator"
 require "i18n"
 
 SafeYAML::OPTIONS[:suppress_warnings] = true
-I18n.config.available_locales = :en
 
 module Jekyll
   # internal requires

lib/jekyll/utils.rb

@@ -203,7 +203,10 @@ module Jekyll
       end
 
       # Drop accent marks from latin characters. Everything else turns to ?
-      string = ::I18n.transliterate(string) if mode == "latin"
+      if mode == "latin"
+        I18n.config.available_locales = :en if I18n.config.available_locales.empty?
+        string = I18n.transliterate(string)
+      end
 
       slug = replace_character_sequence_with_hyphen(string, :mode => mode)