add documentation on how to change language

[BjoernRave]

It would be good if you could explain somewhere what is the best way to switch between languages, maybe even expose a changeLang function in the useTranslation hook

[aralroca]

Ok! For the simple way as possible, you don't need any API of this lib to change the language. You can do it directly with <Link> component or Router.push of next.js.

import React from 'react'
import useTranslation from 'next-translate/useTranslation'

import i18nConfig from '../i18n.json'

function ChangeLanguage() {
  const { t, lang } = useTranslation()

  return i18nConfig.allLanguages.map(lng => {
    if(lng === lang) return null

    const languageName = t(`layout:lang-${lng}`)
     // Or you can attach the current pathame at the end
    const href = `/${lang}`

    return (
      <Link href={href} key={lng}>
        {languageName}
      </Link>
    )
  })
}

We can provide some examples in the docs. But there isn't a changeLang function.

[BjoernRave]

I came up with this function to change the language, I might do a PR to the lib to add this function to useTranslation once I figure out how to access router

  const changeLanguage = (lng: string) => {
    if (router.pathname === "/") {
      router.push(`/${lng}`);
    } else {
      let routes = router.pathname.split("/");
      if (allLanguages.includes(routes[1])) {
        routes[1] = lng;
      } else {
        routes.splice(1, 0, lng);
      }
      router.push(routes.join("/"));
    }
  };

It would also be good to have a Link component which extends the Link Component from next.js, but persists the language on route changes

This is my custom Link Component:

import NextLink, { LinkProps } from 'next/link'
import { useRouter } from 'next/router'
import { FC } from 'react'
import { allLanguages, defaultLanguage } from '../i18n.json'

const Link: FC<LinkProps> = ({ children, href, as, ...props }) => {
  const router = useRouter()

  const getCurrentLanguage = () => {
    if (router.pathname === '/') {
      return defaultLanguage
    } else {
      let routes = router.pathname.split('/')
      if (allLanguages.includes(routes[1])) {
        return routes[1]
      } else {
        return defaultLanguage
      }
    }
  }

  return (
    <NextLink
      href={`/${getCurrentLanguage()}${href === '/' ? '' : href}`}
      as={`/${getCurrentLanguage()}${as}`}
      {...props}>
      {children}
    </NextLink>
  )
}

export default Link

[aralroca]

Ok @BjoernRave, if you do a PR of Link and changeLanguage we can add them to our API. However, I am in favor of do it separately of useTranslation hook, in order to take advantage of tree-shaking. Because in most cases you need to change the language in a modal, and then in all other pages you don't need that extra code. And we want to keep a tiny size of this lib.

Ex of possible imports:

import Link from 'next-translate/Link'
import changeLanguage from 'next-translate/changeLanguage'