To reproduce:

• open Jenkins using the Czech localization

Expected

• correctly encoded links in side panel (e.g. People=Lidé)

Actual

• wrong encoding for items supplied by Core (People=LidĂ©)
• correct encoding for items supplied by plugins (e.g. https://github.com/jenkinsci/lockable-resources-plugin/blob/346d600eea2422ac91d6aa41d91a37723508cfe4/src/main/resources/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction/index_cs.properties#L24 )
• localization coming from the `Messages` classes generated by Localizer seems OK
• correct result in ScriptConsole with 

  ResourceBundle.getBundle("hudson.model.View.sidepanel").getString("People")