Extend plugin languages

Support Plugins
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3

OK, so this works for front-end, but not Admin. I translated Login plugin to LT. Everything is in user/languages/lt.yaml

PLUGIN_LOGIN:
  USERNAME: "Vartotojo vardas"
  EMAIL: "El. paštas"
  USERNAME_EMAIL: "Vartotojo vardas/El. paštas"
  <...>

I also went to my profile (top left of Admin) and changed the language, but still can’t see any changes. And actually none of Admin strings are translated - whole Admin is still in English. What am I missing?