Site subtitle with mulitiple languages


after building a Site with mulitple language content i recogniced that small string i added as a kind of subtitle to the sites title.
For convenience - and because i had no idea how to put this in the yaml or blueprint i took the short way and added it just as a plain formatted string to the base.html.twig.

Could someone give me a description what i should have done instead to get a translated version on other than the default language?

Thank you for any hints