前提・実現したいこと

devise導入後のフラッシュメッセージを日本語表示させたい

発生している問題・エラ〜メッセージ

ログイン画面の左上：　translation missing: ja.devise.failure.user.unauthenticated
ログイン後のトップページ左上：
translation missing: ja.devise.sessions.user.signed_in

該当のソースコード

config/application.rb

require_relative 'boot'

require 'rails/all'

# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)

module GamePlan
  class Application < Rails::Application
    # Initialize configuration defaults for originally generated Rails version.
    config.load_defaults 6.0
    config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}').to_s]
    config.i18n.default_locale = :ja
    # config.i18n.available_locales = [:ja, :en]
    config.time_zone = 'Asia/Tokyo'

    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration can go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded after loading
    # the framework and any gems in your application.
  end
end

Gemfile

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.6.5'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 6.0.0'
# Use mysql as the database for Active Record
gem 'mysql2', '>= 0.4.4'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
# gem 'sass-rails', '~> 5'
# Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
gem 'webpacker', '~> 4.0'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.7'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use Active Model has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use Active Storage variant
# gem 'image_processing', '~> 1.2'

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.4.2', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15'
  gem 'selenium-webdriver'
  # Easy installation and use of web drivers to run system tests with browsers
  gem 'webdrivers'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

gem "haml-rails", ">= 1.0", '<= 2.0.1'
gem 'bootstrap-sass'
gem 'sass-rails'
gem 'devise'
gem 'rails-i18n', '~> 6.0.0'

views/layouts/application.html.haml

!!!
%html
  %head
    %meta{:content => "text/html; charset=UTF-8", "http-equiv" => "Content-Type"}/
    %title GamePlan
    = csrf_meta_tags
    = csp_meta_tag
    = javascript_pack_tag 'application', 'data-turbolinks-track': 'reload'
    = stylesheet_pack_tag 'application', media: 'all', 'data-turbolinks-track': 'reload'
  %body.text-white.bg-dark
    = render 'layouts/header'
    = render 'layouts/notifications'
    = yield

views/layouts/_notifications.html.haml

- flash.each do |key, value|
  = content_tag(:div, value, class: "flash flash__#{key}")

試したこと

・~~rails-i18n', '~~> 5.2.1' ~~　rails-i18n', '~~> 6.0.0' に変更し、bundle update後bundle install（成功）
・application.rb内に以下の記述を追加。
config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}').to_s]
config.i18n.default_locale = :ja
・rails sでサーバーの再起動