[ExperienceStudio] adminUI translations from yaml manifest

* The adminUI translations from yaml manifest seem not to be translatable in a coherent way.
* Some elements pass it through `$t()` on the admin side which suggests it should be a snippet key instead of the plain text.
* Clarify how the adminUI translations should work. Snippet key? Key-value de: {} en: {} ?

Start by tracing the ExperienceStudio YAML manifest translations into the admin side, especially the elements that pass values through $t(). Determine whether the intended convention is snippet keys or locale-specific key-value maps such as de and en. Done means the translation behavior is clearly decided and applied consistently.

Written by the indexing model from the issue text.