Stencil Component Translations

A quick way to set up i18n for Stencil components without dependencies.

Apr 5, 2021

#javascript #typescript #stencil #webdev

Photo by Lucas George Wendt on Unsplash

I have been using the same strategy to internationalize quickly Stencil components without dependencies in various projects. Among others for the project Owlly or the Bonjour foundation.

As all these projects are open source, I will share with you my recipe 🧑‍🍳.


This blog post has not for goal to set up i18n for an application, design system or any other sort of projects from a certain scale. I might blog about this some day too, as I recently internationalized with the help of the community our project DeckDeckGo, but, this article has for goal to add translations to a relatively small component or set of components without dependency.

I use this solution when I create components which contain some slotwith default values and which have has primary market our lovely “four languages + english per default” Switzerland 🇨🇭.


In your project create a new utility translations.util.ts and add the declarations.

interface Translation { [key: string]: string; } interface Translations { de: Translation; en: Translation; }

For this example, I will “only” use German and English. For a real life use case, extend it with your requirements.

I declared an interface Translation but, it can be replaced with a TypeScript Record<string, string> . Result is the same, as you rather like.

Following the declarations, add a constant for the default (fallback) language and a list of supported languages.

const DEFAULT_LANGUAGE: 'en' = 'en'; const SUPPORTED_LANGUAGES: string[] = ['de', 'en'];

Finally, add the effective translations.

const TRANSLATIONS: Translations = { de: { question: 'Wie fühlen Sie sich heute?', super: 'Sehr gut', bad: 'Nicht gut' }, en: { question: 'How do you feel today?', super: 'Super', bad: 'Bad' } };

In this solution, as my goal is to keep it quick and easy, I code the translations.

It is possible to handle these in separate json files and import these dynamically at runtime. That’s two features I have developed for my more complex use case. After all I maybe really need to blog about this? Ping me if you think that would be an interesting subject!

Detect Languages

I did not reinvent the wheel. I had a look to the widely use open source library ngx-translate and implemented its detection of the browser languages.

In the same file, add the following function and initialization of the default language.

const initBrowserLang = (): string | undefined => { if (typeof window === 'undefined' || typeof window.navigator === 'undefined') { return undefined; } let browserLang: string | null = window.navigator.languages && window.navigator.languages.length > 0 ? window.navigator.languages[0] : null; // @ts-ignore browserLang = browserLang || window.navigator.language || window.navigator.browserLanguage || window.navigator.userLanguage; if (typeof browserLang === 'undefined') { return undefined; } if (browserLang.indexOf('-') !== -1) { browserLang = browserLang.split('-')[0]; } if (browserLang.indexOf('_') !== -1) { browserLang = browserLang.split('_')[0]; } return browserLang; } const browserLang: string | undefined = initBrowserLang();


The setup and detection are ready, we need a function to render the translations.

export const translate = (key: string, customLang?: 'de' | 'en'): string => { const lang: string | undefined = customLang || browserLang; return TRANSLATIONS[lang !== undefined && SUPPORTED_LANGUAGES.includes(lang) ? lang : DEFAULT_LANGUAGE][key]; };

It either uses the browser or a parameter language, check it against the list of supported languages or fallback to the default language, and returns the related translations.


In our component, the above function can be used to render a translation.

import { Component, h, Host } from "@stencil/core"; import { translate } from "./translations.utils"; @Component({ tag: "question", shadow: true }) export class Question { render() { return ( <Host> <p>{translate("question")}</p> <slot name="answer">{translate("super", "de")}</slot> </Host> ); } }

It renders text, with or without specifying a language, and can be used with slot too.


That was my small quick recipe to set up i18n to a relatively small set of components. I hope it is useful and if you think I should share the more complex solution in another post, let me know.

To infinity and beyond!