Internationalization of FastAPI

There are a lot of solutions to attach gettext to FastAPI, for example, I used this article.

The problem is that they all translate the text immediately, but I need to store it in the pydantic model and translate it into the user's language at the time of serialization, i.e. lazy evaluation

I had to do a bit of cycling and this is what I came up with:

class LazyGettext(BaseModel):
    message: str
    params: dict = Field(default_factory=dict, exclude=True)
    syntax: str = None

    def __mod__(self, params):
        self.params = params
        self.syntax = 'mod'
        return self

    def format(self, **kwargs):
        self.params = kwargs
        self.syntax = 'format'
        return self

    def __repr__(self) -> str:
        return self.__str__()

    def __str__(self) -> str:
        wrapper = TranslationWrapper()  # класс из статьи, ссылка на кот-орую выше
        tpl = wrapper.translations.gettext(self.message)
        if self.syntax == 'mod':
            tpl = tpl % self.params
        elif self.syntax == 'format':
            tpl = tpl.format(**self.params)
        return tpl

    @model_serializer
    def serialize(self):
        return self.__str__()

      
def _(message: str) -> LazyGettext:
    return LazyGettext(message=message)

# Пример использования

class Event(BaseModel):
    message: str | LazyGettext


events = [
    Event(messag=_('User {user} woke up').format(user="test")),
    Event(messag=_('User {user} commuted suicide').format(user="test")),
]

@router.get("/events/")
async def game_events(
) -> List[Event]:
    # С соотв. middleware будет выдавать текст на нужно языке в зависимости
    # от http заголовками
    return events

      

I don't like that for each line you have to build a whole model, I wanted to do it through pydantic string typesbut something didn’t work out right away.

Maybe someone can recommend a better solution? Fastapi-localization seems to have some kind of lazy wrapper, but I don't understand how to use it.