What "Roger" means? Is this a translation error or...?

[Sasarai10]

When you recruit Meg and Gadget....after recruiting them,Gadget says "Roger" when Meg says "Let's go"

What that "Roger" means exactly?

[Wolkendrache]

It's not an error, it means "Alright!" or "I understand!" or "OK!" or "Aye!" or so.
I've read that it came from radiocommunication: when a message was received, they would say "roger", something like that.

[Pyriel]

Yeah, it mainly means "message received and understood". If memory serves, it's actually just a remnant of an older radiotelephony alphabet where "Roger" stood for R the way "Romeo" does now (similar to how "Whiskey Tango Foxtrot" stands for "WTF" if you're more familiar with that). The whole point is just that the words in the alphabet are terse, and harder to mishear over the radio, so saying "roger" might go amiss less often than saying "received".

The military used it initially in communications, so "roger" could be the response to being ordered to fire missiles at a hospital, or to someone telling you there's ice cream in the mess hall for you. Nowadays it's a common term in all sectors. It still has a similar gamut though, i.e. ice cream or time to go to a funeral, but people mostly use it when they want to sound sort of military or official or mechanical, as is probably the case here.

[Omnigamer]

Obligatory:

https://www.youtube.com/watch?v=fVq4_HhBK8Y

[Metsu]

In the japanese version, I am sure Gadget said 了解　（りょうかい） or "ryoukai" as we would spell it. It is essentially the same and used in Japanese like "I understand!" or in military or radio communication "Yes sir!" or "Roger!".