python i18n sample with fastapi, gettext, contextvars

sample code for implementing i18n in a fastapi/starlette (or whatever python framework (or whatever python software))

in this implementation we use python's gettext module and locale directories with .po .mo files (like how django does it)

useful links related to this topic:

https://docs.python.org/3.12/library/gettext.html

https://docs.python.org/3/library/contextvars.html

https://peps.python.org/pep-0567/

https://docs.djangoproject.com/en/4.2/topics/i18n/translation/

Kludex/starlette#420

https://github.com/tomwojcik/starlette-context

• django also uses contextvars for translation stuff

https://github.com/django/asgiref/blob/main/asgiref/local.py

https://github.com/django/django/blob/b34a4771a3d4cd7829a1f38a0f6a7a0da519a724/django/utils/translation/trans_real.py#L368

start to translate

0- install gnu gettext to access msgfmt, xgettext, msgmerge tools

1- create/update language .po file

make LANG=fa makemessages

2- translate messages in locales/fa/LC_MESSAGES/messages.po

3- compile translation to .mo file

make LANG=fa compilemessages

Run the app

python app.py

and here is an extremely sophisticated functional test:

curl -X 'GET' \
  'http://127.0.0.1:8000/' \
  -H 'accept: application/json' \
  -H 'accept-language: fa'

• response should be like this

[
  "سلام دنیا",
  "بله",
  "خیر",
  "خاک بر سر اسرائیل از خدا بی‌خبر :هندونه:"
]