Problem

If you try to change meta or robots information in the promote panel on the home page you will get a SEO url validation error.

Steps to reproduce

create a new database with language german and with demo data
install the website_seo module
activate the developer mode
go to Settings -> Translations -> Languages and set the "Short code" to "en" for the "English" entry
go to Website Admin -> Configuration and add "German / Deutsch" as second language ans as default language and save
go to the home page in the frontend, open the promote panel, change the meta title or meta description or robots content and save: you will get the error "Invalid SEO URL. The allowed characters are a-z, A-Z, 0-9, - and _." and nothing will be saved
Expected behaviour
the meta title, meta description and robots content should also be changeable in the promote panel on the home page