You can customize site texts and theme translations without changing your user locale. Both interfaces offer a dropdown to select the language.
But the interface for editing templates does not offer a way to select a language
This not only means that you have to change your interface language several times when you want to edit the template in multiple languages, but it also makes it much easier to forget that editing one version is not enough to ensure that all users receive the desired message. I think a dropdown like in the other interfaces could improve that.