setLocale not working in useEffect about a18n

[FallenMax]

@zitanlin Hi, can you provide a minimal reproducible repo?

Please note that a18n.setLocale() & a18n.addLocaleResource() only change output of a18n calls like a18n("someText") and does nothing else. In order for new language/translation take effect, you need ensure your app is re-rendered using texts newly returned by a18n("someText").

For static text (i.e. not re-generated between render), they might be bound to stale translations. See https://github.com/FallenMax/a18n#1-why-is-it-important-to-load-translation-resources-and-specify-a-locale-before--all-other-code-is-run for detail. In these situations, you'll have to window.reload() and set correct language before app code execute.

[zitanlin]

@FallenMax Simple demo：https://github.com/zitanlin/a18n-test.git

I have two problems as follow：

1. switch language in useEffect
2. Dynamically switch languages ​​in the page

[FallenMax]

https://github.com/zitanlin/a18n-test/blob/master/src/App.js#L15-L17

  const changeLanguage = async () => {
    const temp = language === 'zh' ? 'en' : 'zh';
    setLanguage(temp);
    await a18n.setLocale(temp); // moving this line up fixes the problem
    await a18n.setLocale(temp);  // this line is unnecessary, also `await` is not required
  };

@zitanlin Hi, the problem is that setLanguage is called before a18n.setLocale(temp), this means that react could re-renders this component BEFORE a18n is set to use new language.
As mentioned in comment, moving a18n.setLocale(temp) before setLanguage fixes this problem (await is not required and should be removed).

Hope this helps!

[zitanlin]

https://github.com/zitanlin/a18n-test.git

`const [language, setLanguage] = useState('zh');
useEffect(async () => {
console.log('---- use effect = ', language)
a18n.setLocale('zh');
}, []);

const changeLanguage = async () => {
console.log('--- language = ', language);
const temp = language === 'zh' ? 'en' : 'zh';
a18n.setLocale(temp);
setLanguage(temp);
};
`

1. setLocale in useEffect function not working. I setLocale('zh') in useEffect, but not working. for example:
   

2. it does not switch to expected language at first call changeLanguage function, then it works. You can test it.

[zitanlin]

@FallenMax

[FallenMax]

@zitanlin

a18n is a general i18n library, and it does not know about React or any other UI framework. This means a18n.setLocale() alone won't do anything about your app UI. As mentioned in previous comments, you need to trigger app re-render somehow after a18n.setLocale(), so that latest language can be applied.

In your case, you should call setLanguage after a18n.setLocale().

[zitanlin]

@FallenMax Got it, thank you very much！