import React from 'react';
import { Trans, useTranslation } from 'react-i18next'
​
function MyComponent() {
  const { t } = useTranslation('myNamespace');
​
  return <Trans t={t}>Hello World</Trans>;
}

import React from 'react';
​
function MyComponent({ person, messages }) {
  const { name } = person;
  const count = messages.length;
​
  return (
    <div>
      Hello <strong title="this is your name">{name}</strong>, you have {count} unread message(s). <Link to="/msgs">Go to messages</Link>.
    </div>
  );
}

import React from 'react';
import { Trans } from 'react-i18next'
​
function MyComponent({ person, messages }) {
  const { name } = person;
  const count = messages.length;
​
  return (
    <Trans i18nKey="userMessagesUnread" count={count}>
      Hello <strong title={t('nameTitle')}>{{name}}</strong>, you have {{count}} unread message. <Link to="/msgs">Go to messages</Link>.
    </Trans>
  );
}

"userMessagesUnread": "Hello <1>{{name}}</1>, you have {{count}} unread message. <5>Go to message</5>.",
"userMessagesUnread_plural": "Hello <1>{{name}}</1>, you have {{count}} unread messages.  <5>Go to messages</5>.",

<Trans
  i18nKey="myKey" // optional -> fallbacks to defaults if not provided
  defaults="hello <italic>beautiful</italic> <bold>{{what}}</bold>" // optional defaultValue
  values={{ what: 'world'}}
  components={{ italic: <i />, bold: <strong /> }}
/>

<Trans i18nKey="welcomeUser">
  Hello <strong>{{name}}</strong>.
</Trans>
// JSON -> "welcomeUser": "Hello <1>{{name}}</1>.",
<Trans i18nKey="multiline">
  Some newlines <br/> would be <br/> fine
</Trans>
// JSON -> "multiline": "Some newlines <1/> would be <3/> fine"

const person = { name: 'Henry', age: 21 };
const { name, age } = person;
​
<Trans>
  Hello {{ name }}. // <- = {{ name: name }}
</Trans>
// Translation string: "Hello {{name}}"
​
​
<Trans>
  Hello {{ firstname: person.name }}.
</Trans>
// Translation string: "Hello {{firstname}}"

const messages = ['message one', 'message two'];
​
<Trans i18nKey="newMessages" count={messages.length}>
  You got {{ count: messages.length }} messages.
</Trans>
​
// Translation strings:
// "newMessages": "You got one message."
// "newMessages_plural": "You got {{count}} messages."

<Trans i18nKey="list_map">
  My dogs are named:
  <ul i18nIsDynamicList>
     {['rupert', 'max'].map(dog => (<li>{dog}</li>))}
  </ul>
</Trans>
// JSON -> "list_map": "My dogs are named: <1></1>"

<Trans
  i18nKey="myKey" // optional -> fallbacks to defaults if not provided
  defaults="hello <0>{{what}}</0>" // optional defaultValue
  values={{ what: 'world'}}
  components={[<strong>univers</strong>]}
/>

<Trans i18nKey="userMessagesUnread" count={count}>
    Hello <strong title={t('nameTitle')}>{{name}}</strong>, you have {{count}} unread message. <Link to="/msgs">Go to messages</Link>.
</Trans>

"Hello <1>{{name}}</1>, you have {{count}} unread message. <5>Go to message</5>."

Trans.children = [
  'Hello ',                           // index 0: only a string
  { children: [{ name: 'Jan'  }] },   // index 1: element strong -> child object for interpolation
  ', you have',                       // index 2: only a string
  { count: 10 },                      // index 3: just object for interpolation
  ' unread messages. ',               // index 4
  { children: [ 'Go to messages' ] }, // index 5: element link -> child just a string
  '.'
]

i18next.init({
  // ...
  react: {
    // ...
    hashTransKey: function(defaultValue) {
      // return a key based on defaultValue or if you prefer to just remind you should set a key return false and throw an error
    },
    defaultTransParent: 'div', // a valid react element - required before react 16
    transEmptyNodeValue: '', // what to return for empty Trans
    transSupportBasicHtmlNodes: true, // allow <br/> and simple html elements in translations
    transKeepBasicHtmlNodesFor: ['br', 'strong', 'i'], // don't convert to <1></1> if simple react elements
    transWrapTextNodes: '', // Wrap text nodes in a user-specified element.
                            // i.e. set it to 'span'. By default, text nodes are not wrapped.
                            // Can be used to work around a well-known Google Translate issue with React apps. See: https://github.com/facebook/react/issues/11538
                            // (v11.10.0)
  }
});