OK, please go to File -> Setup -> User profiles, backup your current user profile (export). Then load a profile from the Studio installation folder (c:\program files...) and check again.

The only effect from the app was that it prevented my alternative CAT tool from launching with an error message saying something about wrong syntax in manifest.xml file and SideBySide issues (have no idea what sort of error it is).
After several hours of watching youtube and reading articles, I gave up and was about to reinstall my Windows. As a last resort, I decided to visit that magic app again [to say goodbye] and noticed that its Apply button changed to Undo. I pressed Undo. This removed the SideBySide  error and recovered my alternative CAT tool after reboot. Thank god. Now I came to status quo as before my vain efforts.
Just now I found this thread. Matthew Docherty described a similar, if not same, issue. Unfortunately, I did not find his question before I posted mine... It could save me time.
Nevertheless, thank you Jerzy and Nora for your input.

Jerzy Czopik said:

BTW, Windows looks perfect with 100% and not good with 150%, it is all too huge then...

Compare this. With my normal vision (I don't wear glasses or lens), I can hardly read time and date in the right bottom corner. No, 100% scaling is not acceptable for me.

Well, I wear glasses and prefer 100%, certainly. A screenshot does not represent exactly what you see, but even with the very high resolution of MS Surface 100% is better. You can simply bring more necessary information on the screen in these parts of programs, which are really important. In Studio for example, this is the editor, terminology recognition, translation results, error messages and termbase viewer. With a bigger scaling I would not be able to place all this on a single screen, but when using 100% I have this and can still work comfortable, as the text shown in Studio is big enough. Menus, however, are fully unimportant - I don't need to read their descriptions, as what I use is well placed with big symbols or can be accessed with shortcuts.

Then you should have bought a device with sensible display size, appropriate for the display resolution, in the first place.

This all is a consequence of the stupid trend of extremely high resolutions (4K) on stupidly small displays (starting with 13"!!!)

1920 x 1080 resolution is sensible on 24" display.
2560 x 1440 resolution is sensible on 32' display.
3840 x 2160 resolution is sensible on 48" display (acceptable on 43" display).

Period.

Anything else is total nonsense.
Because the only sensible reason for higher resolution is to get more information on the screen...
And turning on scaling - because one can barely see anything on small displays with high resolutions - defeats this purpose completely!

Even Polenka: how comes, that you know the absolute truth? How comes, that only these and no other screen resolutions are feasible? Will you forbid other (like myself) to chose whatever we like? Are you some kind of Adolf Hitler here to dictate us your own opinion?

Sorry, but your post is highly irritating. Your own opinion may very well apply to your own business, but treating us like idiots just because we do not agree with your opinion is far beyond your competences. Even if I quite often agree with your opinion re professional attitude, your way to communicate is unacceptable here. Please stop treating other like idiots and keep your opinions for yourself.

If you are part of the minority which is OK with high resolution on small displays, then everything is okay.
You are not moaning, you do it on purpose and you are fine with what you get.

My statement applies to the vast majority of people which are negatively affected by the trend, i.e. those which are basically forced to turn on scaling because they can't see properly the miniature fonts on 100% scaling... and then are moaning around.

Personally, I used 1024 x 768 on a 14" CRT back in the 90's and everybody was saying it's not acceptable because it was too small for them.
So what? I did it on purpose and I was happy with that. If I would be moaning about that, then I would be to blame because the normal resolution on that display size at that time was 800 x 600.

BTW, it's not my opinion, it's just a pure mathematics.

1920 x 1080 on a 15" notebook was a standard for quite some time... and it was so-so to use, to be able to read the text.
So, what's the logic behind putting like double resolution on even smaller screen?!

There is only one "logic" - money...
Convince people that these "retina" displays are something they really really really MUST have... and then make money on them.

If I'm honest, I never thought about such details. Usually, I just come at a hardware store, choose a device and buy it. I don't buy overexpensive devices, and I don't think my monitors are 4K. And yes, you are right: I don't need to get more information on the screen. If I had an on-screen soccer field, I could build a soccer stadium with infrastructure around it. I mean I have plenty of unused space with 100% scaling [and hardly visible details]. That is why I use 150% scaling. It has never been a problem when I used Win7 or earlier versions. Neither for Studio nor for any other software elements, they all worked fine.

I have Studio 2017 on my second PC with Win7. I checked it right now: I use 125% scaling there. Weirdly, 125% is enough to make icons and captions clearly visible and keep the Studio windows within the screen limits with Windows 7. But with Windows 10, 125% is not enough. I cannot explain this.
Whatever... Thank you all for your sincere attempt to help.

Anyway, Stepan, looking at your first screenshot I don't think this is related to scaling anyway...

The thing is, the dialog in fact does NOT go off-screen... it's just the way you created the screenshot which looks like it goes "below the screen".
It looks like Studio - or that particular dialog only, perhaps - just uses the entire screen height instead of deducting the taskbar height.

I've seen this issue with other applications too... and I don't know the solution. :-\

E.g. I think(!) that Office applications when not displayed fullscreen, tend to go "beyond/underneath the taskbar", but when turned fullscreen, they behave correctly.

EDIT: Heh, is this your screenshot in this 3 years old thread? ;-)
answers.microsoft.com/.../ae6ca822-7f4b-47a4-a4a0-28fb5e024433