accounts-frontend/packages/app/services/i18n/i18n.ts

import { IntlShape, createIntl, createIntlCache } from 'react-intl';
import captcha from 'app/services/captcha';
import locales from 'app/i18n';

import intlPolyfill from './intlPolyfill';

export const SUPPORTED_LANGUAGES = Object.keys(locales);
export const DEFAULT_LANGUAGE = 'en';

function getBrowserPreferredLanguages(): string[] {
    return ([] as string[]).concat(navigator['languages'] || []).concat(navigator['language'] || []);
}

function detectLanguage(userLanguages: string[], availableLanguages: string[], defaultLanguage: string): string {
    return (
        userLanguages
            .map((lang) => (lang.split('-').shift() || '').toLowerCase())
            .find((lang) => availableLanguages.indexOf(lang) !== -1) || defaultLanguage
    );
}

const cache = createIntlCache();

let intl: IntlShape;

class I18N {
    detectLanguage(lang: string = ''): string {
        return detectLanguage(
            [lang].concat(getBrowserPreferredLanguages()).filter((item) => !!item),
            SUPPORTED_LANGUAGES,
            DEFAULT_LANGUAGE,
        );
    }

    getIntl(): IntlShape {
        if (!intl) {
            intl = createIntl(
                {
                    locale: 'en',
                    messages: {},
                },
                cache,
            );
        }

        return intl;
    }

    async changeLocale(locale: string = DEFAULT_LANGUAGE): Promise<IntlShape> {
        const { messages } = await this.require(locale);

        captcha.setLang(locale);

        intl = createIntl(
            {
                locale,
                messages,
            },
            cache,
        );

        return intl;
    }

    async ensureIntl() {
        await intlPolyfill('en');
    }

    async require(
        locale: string,
    ): Promise<{
        locale: string;
        messages: Record<string, string>;
    }> {
        const [{ default: messages }] = await Promise.all([
            import(/* webpackChunkName: "locale-[request]" */ `app/i18n/${locale}.json`),
            intlPolyfill(locale),
        ]);

        return {
            locale,
            messages,
        };
    }
}

export default new I18N();