The best private operating system for journalists is the "Olivetti Lettera 22" [1].

* Cross-Platform

* Multi-Language

* Offline

* Room Protection

For extra security, you can use an external data disposal tool [2].

[1] https://en.wikipedia.org/wiki/Olivetti_Lettera_22

[2] https://geekyget.com/products/hand-shredder/