All the nodes of my Hebrew site using Drupal 8 have this problem: Their address is similar to www.example.com/he/node/1, instead of what I was used to in Drupal 6+7 that was www.example.com/node/1. The difference is that now the URLs contain /he/ which I have never added.
It happens even when a node (whenever written in Hebrew or English) has its language set to English or Not specified.
What I tried is the following:
At the start all, my nodes were set to Hebrew so I thought it could be the behavior of the new language system of Drupal 8. I thus changed all nodes written for English speaking audience from Hebrew to English; I flushed the cache, but it didn't help: These nodes still had /he/ in their URLs.
I thought the Alternative hreflang module could cause this, so I removed it, but the problem persisted after flushing the cache.