Thank you @sfusato for the reply. It is very much appreciated. So, at the end I had to make a couple of changes:
1 In config.exs:
config :myApp, MyAppWeb.Gettext, locales: ~w(en fr es)
Not sure why but it seems that ll_CC format may cause issues. For what I understood in gettext doc that was the suggested format. But I could not make it work, so I just made my life simpler using only the language code without the country.
2 Then the command that did it for me was:
mix gettext.merge priv/gettext --locale fr
mix gettext.merge priv/gettext --locale es
3 After that a simple (as mentioned by @sfusato mix gettext.extract --merge updates any change in the pages.
I am leaving it here in case it helps to anyone else in the future.
Thanks
