Scheinsicherheit (ger) -> pseudo safety?

In German we have the word "Scheinsicherheit", meaning that you are applying some measures and feel protected against some threats. However if such a threat might occur in reality these safety measures might turn out to be useless.

E.g. installing some backup-software on your PC, without noticing that the data from the backup cannot be restored if needed due to programming errors.

How would you phrase that in English: e.g. pseudo-safety??

I'd call it a "false sense of security". This phrase is fairly common, and in fact security is by far the most popular word appearing after "false sense of": See Ngrams.

This doesn't fit precisely with your example, but there is also the concept of security theatre, which is where you set up safeguards meant to provide some measure of security, but the safeguards are arguably just for show.

Examples:

• Making passengers remove their shoes when boarding a plane, in case of a shoe bomb: it's theatre because the shoe-bomb is unlikely to be a workable threat, and there are other places one could hide a bomb of that size, but because someone once tried to detonate a shoe bomb, the airport security check all shoes now (while not applying any extra scrutiny to other things).

• safety seals on food/drugs: Ostensibly these are meant to demonstrate that the product hasn't been tampered with. These were introduced after the big scare involving adulterated Tylenol drugs. It's security theatre because it's relatively easy to adulterate the drugs and replace the seals, given enough patience and time. You can't just do it in the store, but you can still do it.

Security theatre is meant to provide a sense of security but it doesn't actually achieve its stated goals of making you safer.