1. Add a parameter to a host, key 'languages', values should contain a non-English character, for example: Español, English, 日本語
2. Make sure this host has an operating system whose templates print this parameter. You can simply create a new template with content: "<%= @host.params['languages'] %>"
3. Review the template, you can go to the tab 'Templates' on the Host view and click on 'Review' under 'Edit' next to the template you want.
4. The parameter should be resolved as: "Español, English, 日本語" , instead it is resolved as "Español, English, 日本語"

Originally from: http://serverfault.com/questions/615937/foreman-parameters-accents-not-allowed?rq=1