Expose public translations to the client

[phorward]

To implement client-side translations, there must be a way to expose translations of a given language to the client.

In several customer projects, it was done like this already:

    @exposed
    @as_json_response
    def get_current_translations(
        self,
        *,
        all_langs: bool = False,
        v: str | None = None,
    ) -> dict[str, str] | dict[str, dict[str, str]]:
        if (
            not (conf.debug.disable_cache and current.request.get().disableCache)
            and any(os.getenv("HTTP_HOST", "") in x for x in conf.i18n.domain_language_mapping)
        ):
            # cache it 7 days
            current.request.get().response.headers["Cache-Control"] = f"public, max-age={7 * 24 * 60 * 60}"
        if all_langs:
            return {
                lang: {tr_key: str(translate(tr_key, force_lang=lang))
                       for tr_key, values in systemTranslations.items()}
                for lang in conf.i18n.available_dialects
            }
        return {tr_key: str(translate(tr_key)) for tr_key, values in systemTranslations.items()}

This is both very non-performant, but also reveals translations of - maybe internal parts - publicly to any client.

An idea to resolve this would be to work either with a prefix, or with a public-flag on translations.