Below you will find the direct links to download the language pack depending on your digital storefront. Do not download suspicious EXE files from third-party websites. Only use the official store links.
If the automatic DLC download fails, you can force the download via the Steam Console (Advanced method): atomic heart spanish language pack link
Some users in Asia or South Africa report that the pack is hidden. Fix: Change your Steam/Windows region to Spain or Mexico temporarily. Restart the client, download the 3GB pack, then change back. Below you will find the direct links to