Any word with a space is merged into each other

This issue is caused by an outdated resource pack.
If you are the pack creator, you need to add a space provider to your default.json font. If any other providers used a space character as a placeholder, you should instead use \u0000. Remember that if your font file doesn't have any changes compared to vanilla, you don't need to include it in your pack.
If you are the pack user, look for a new download of the pack or contact the creator.