csv2i18n.rb

require 'csv'

translations = Hash.new { |h, k| h[k] = Hash.new(&h.default_proc) }
headers = ['key', 'ja', 'en', '...']

CSV.open('i18n.csv', 'r', col_sep: "\t", headers: true) do |csv|
  csv.each do |row|
    locales = csv.headers - ['key']

    locales.each do |locale|
      keys = [locale, row['key'].split('.')].flatten.map(&:to_sym)
      last_key = keys.pop

      translations.dig(*keys)[last_key] = row[locale]
    end
  end
end

translations.each do |locale, _translations|
  File.write("config/locales/#{locale}.yml", _translations.to_yaml)
end