Make translations loading thread-safe

[mensfeld]

close #643

[chaadow]

hi @mensfeld I had an issue with loading not being thread safe:

basically since eager load is disabled, two sidekiq threads are trying to load I18n at the same time resulting into this

I'm going to eager load at bootup, but was wondering if I can just do

MUTEX.synchronize do
  Utils.deep_merge!(translations[locale], data)
end

or maybe add the synchronize here:

i18n/lib/i18n/backend/base.rb

Line 247 in f2fb6a5

data.each { |locale, d| store_translations(locale, d || {}, skip_symbolize_keys: keys_symbolized) }

or wrap the entire store_translations into a synchronize.

what do you think is the best way please 🙏🏼 ( i wanna ask a real person, i dont wanna ask an AI. ty so much)

[chaadow]

I went ahead and created this PR: #729