Introduce translations and translate library for internationalization

src/languages/en.js

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+export default {
+    hello: 'Hello',
+};

src/languages/es-ES.js

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+export default {
+};

src/languages/es.js

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+export default {
+    hello: 'Hola',
+};

src/languages/translations.js

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+import en from './en';
+import es from './es';
+import esES from './es-ES';
+
+export default {
+    en,
+    es,
+    'es-ES': esES,
+};

src/libs/translate.js

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+import lodashGet from 'lodash.get';
+import Str from 'expensify-common/lib/str';
+import Log from './Log';
+import Config from '../CONFIG';
+import translations from '../languages/translations';
+
+/**
+ * Return translated string for given locale and phrase
+ *
+ * @param {String} locale eg 'en', 'es-ES'
+ * @param {String|Array} phrase
+ * @param {Object} variables
+ * @returns {string}
+ */
+function translate(locale, phrase, variables = {}) {
+    const localeLanguage = locale.substring(0, 2);
+    const fullLocale = lodashGet(translations, locale, {});
+    const language = lodashGet(translations, localeLanguage, {});
+    const defaultLanguage = lodashGet(translations, 'en', {});
+
+    let translationValue;
+
+    // Search phrase in full locale
+    translationValue = lodashGet(fullLocale, phrase);
+    if (translationValue) {
+        return Str.result(translationValue, variables);
+    }
+
+    // Phrase is not found in full locale, search it in language
+    translationValue = lodashGet(language, phrase);
+    if (translationValue) {
+        return Str.result(translationValue, variables);
+    }
+    if (localeLanguage !== 'en') {
+        Log.alert(`${phrase} was not found in the ${localeLanguage} locale`, 0, {}, false);
+    }
+
+    // Phrase is not translated, search it in default language (en)
+    translationValue = lodashGet(defaultLanguage, phrase);
+    if (translationValue) {
+        return Str.result(translationValue, variables);
+    }
+
+    // Phrase is not found in default language, on production log an alert to server
+    // on development throw an error
+    if (Config.IS_IN_PRODUCTION) {
+        const phraseString = Array.isArray(phrase) ? phrase.join('.') : phrase;
+        Log.alert(`${phraseString} was not found in the en locale`, 0, {}, false);
+        return phraseString;
+    }
+    throw new Error(`${phrase} was not found in the default language`);
+}
+
+export {
+
+    // Ignoring this lint error in case of we want to export more functions from this library
+    // eslint-disable-next-line import/prefer-default-export
+    translate,
+};

tests/unit/TranslateTest.js

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+const translate = require('../../src/libs/translate');
+const translations = require('../../src/languages/translations');
+const CONFIG = require('../../src/CONFIG');
+
+translations.default = {
+    en: {
+        testKey1: 'English',
+        testKey2: 'Test Word 2',
+        testKey3: 'Test Word 3',
+        testKeyGroup: {
+            testFunction: ({testVariable}) => `With variable ${testVariable}`,
+        },
+    },
+    es: {
+        testKey1: 'Spanish',
+        testKey2: 'Spanish Word 2',
+    },
+    'es-ES': {testKey1: 'Spanish ES'},
+};
+
+describe('translate', () => {
+    it('Test present key in full locale', () => {
+        expect(translate.translate('es-ES', 'testKey1')).toBe('Spanish ES');
+    });
+
+    it('Test when key is not found in full locale, but present in language', () => {
+        expect(translate.translate('es-ES', 'testKey2')).toBe('Spanish Word 2');
+        expect(translate.translate('es', 'testKey2')).toBe('Spanish Word 2');
+    });
+
+    it('Test when key is not found in full locale and language, but present in default', () => {
+        expect(translate.translate('es-ES', 'testKey3')).toBe('Test Word 3');
+    });
+
+    test('Test when key is not found in default', () => {
+        expect(() => translate.translate('es-ES', 'testKey4')).toThrow(Error);
+        expect(() => translate.translate('es-ES', ['a', 'b', 'c'])).toThrow(Error);
+    });
+
+    test('Test when key is not found in default (Production Mode)', () => {
+        const ORIGINAL_IS_IN_PRODUCTION = CONFIG.default.IS_IN_PRODUCTION;
+        CONFIG.default.IS_IN_PRODUCTION = true;
+        expect(translate.translate('es-ES', 'testKey4')).toBe('testKey4');
+        expect(translate.translate('es-ES', ['a', 'b', 'c'])).toBe('a.b.c');
+        CONFIG.default.IS_IN_PRODUCTION = ORIGINAL_IS_IN_PRODUCTION;
+    });
+
+    it('Test when translation value is a function', () => {
+        const expectedValue = 'With variable Test Variable';
+        const testVariable = 'Test Variable';
+        expect(translate.translate('en', 'testKeyGroup.testFunction', {testVariable})).toBe(expectedValue);
+        expect(translate.translate('en', ['testKeyGroup', 'testFunction'], {testVariable})).toBe(expectedValue);
+    });
+});