Revert "lazy-loading locale I18n backend"

[wjordan]

Reverts #18315.

Failing UI tests with i18n-test errors:

[i18n]
[i18n] expected: "Ok, this is just like the last puzzle, but you need to remember how you used the \"if\" block and the \"repeat\" block together."
[i18n]      got: "Vale, esto es como el último rompecabezas, pero tienes que recordar cómo usaste el bloque \"si\" y el bloque \"repetir\" juntos."
[i18n]
[i18n] (compared using ==)
[i18n]  (RSpec::Expectations::ExpectationNotMetError)
[i18n] ./features/support/browser_helpers.rb:18:in `element_has_i18n_text'
[i18n] ./features/step_definitions/steps.rb:562:in `/^element "([^"]*)" has "([^"]*)" text from key "((?:[^"\]|\.)*)"$/'
[i18n] ./features/support/hooks.rb:45:in `call'
[i18n] ./features/support/hooks.rb:45:in `block in <top (required)>'
[i18n] features/i18n.feature:8:in `Then element ".csf-top-instructions p" has "es" text from key "data.level.instructions.maze_2_14"'