TCA translatable

will close #18276 (closed)

• understand the current status of things and do whatever needs to be done for translators to be able to translate. Maybe that's just refresh-translations?
• do some sanity check to what boyska did:
  • is it correct that tails is the translation domain for TCA?
  • do translators need some kind of hint to understand that the strings they are translating refer to TCA? how can we give them such hints?
  • anything else that seems wrong?
• identify strings that are not translatable and report them (or fix them: sometimes it's just matter of adding _ to the code