Hello friends! Do you find it strange that DICE is looking for Actionscript 2 and 3 UI Software Engineer for Frostbite engine? IIRC Flash is dead. 
https://www.disabledperson.com/jobs/10999821-ui-software-engineer-frostbite-commons
https://www.velvetjobs.com/job-posting/ui-software-engineer-frostbite-commons-101622-484454
and as beginner I wonder how they mixing editor (what is written on c#) with AS3 and c++? I know only about C# + WPF combination.
Also I'm going to develop my own engine and I started to think about how to make such editor and GUI like Frostbite has.
Thanks!!

Scaleform is/was a standard UI tool for games, and it uses Flash/Actionscript.

I don't see them mentioning C# there. But even if they did use C#, it's not a big deal. An experienced programmer is expected to know multiple languages and adapt to new ones as needed.

Frostbites various tools are written in C# using WPF, like Kylotan says there are some action script driven game UI frameworks which is probably where AS comes in rather than for the editor it's self.

They use .net + C#/IronPython + WPF for their frostbite editor, so almost all the authoring tools (level editors, content editors etc...) are written in C# + Python running on top of .net and WPF is their windowing library of choice.

Here is a cool vid/presentation about it:

About AS* script: as Kylotan said so, Scaleform is/was a standard UI tool for games. As I know there is/was a fully fledged unreal engine (both for v3 and I think one probably exists for v4) integration and was the UI tool choice for many developers using unreal engine 3(/4?).
EA before starting to push frostbite as an internal engine for all their bigger studios was using unreal engine for various projects.

Jemme ninja !

7 hours ago, Kylotan said:

I don't see them mentioning C# there.

Frostbite editor is written on C#, but a core of an engine (rendering system jobs, game code) on C++. Also I guess their subsystems c++ based too. 

"Our tools are written primarily in C# and Python; as the editor communicates closely with the engine pipeline you will also delve into C++ pipeline code on a regular basis."

http://www.dice.se/jobs/positions/dice-stockholm-code-senior-tools-engineer/

Also as you can see their tool's codebase in quite massive
https://twitter.com/repi/status/905815895246860288

11 hours ago, Kylotan said:

Scaleform is/was a standard UI tool for games, and it uses Flash/Actionscript.

but Scaleform is dead too or it somewhere between the life and death. 
And I don't see here any Scaleform mention
http://www.mobygames.com/game/windows/battlefield-1/credits
I don't even see Havok here

They used scaleform in some of there older games so maybe they still need to support it? but there modern games mostly likely use a custom framework?

1 hour ago, Jemme said:

They used scaleform in some of there older games so maybe they still need to support it? but there modern games mostly likely use a custom framework?

yes, it's seems like they still using scaleform
http://www.mobygames.com/game/windows/plants-vs-zombies-gw2/credits
but why every credits of every title differ each other - some titles have a lot middleware and open source libs, but some just a few or none.
There is no defined standard for credits?

A lot here
http://www.mobygames.com/game/windows/mass-effect-andromeda/credits

but none here
http://www.mobygames.com/game/windows/star-wars-battlefront_/credits

DICE and EA are very strange guys. It's very hard to see what software and libs they using because of that.

Different studios have different programmers and skills, they probably allow them to work with what there comfortable using.

I emailed Jason Gregory recently about tool chains, because it's relevent I'll share his responce.

21 hours ago, Michael Davidog said:

I started to think about how to make such editor and GUI like Frostbite has.

Some of the first steps are to hire a large team of experienced editor-developers, and spend several million dollars over multiple years on technology developed across multiple studios around the globe.

EA has an enormous body of tech tools and libraries that cover just about anything you want. They've been built up for game after game, from project to project for decades.  When I was working there I noticed and pointed out a date in a comment. It was from nearly two decades earlier, the comment stated that it was the third rewrite and they were hoping it would be the version that would solve all their issues.  The tool worked great, we were adding our own useful bit of functionality which would be added to the suite.