There is a gatsby-plugin-i18n community plugin that you could "use [...] with a response-intl, i18next or any other i18n library. This plugin does not translate messages, it just creates routes for each language, and you can use different layouts for each language if you want. " (quoting the README plugin).
Its first release is dated August 30, 2017, so maybe you have already stumbled upon it ?!
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