Your structure is incorrect. It should be:
content/
├── en/
│ ├── posts/
│ │ ├── post-1.md
│ │ └── post-2.md
│ └── _index.md
└── es/
├── posts/
│ ├── post-1.md
│ └── post-2.md
└── _index.md
config.toml
[permalinks]
posts = '/:year/:month/:day/:title'
[languages.en]
contentDir = 'content/en'
languageName = 'English'
weight = 10
[languages.es]
contentDir = 'content/es'
languageName = 'Spanish'
weight = 20
Also, please read:
https://discourse.gohugo.io/t/sharing-code-in-the-forums/8968