I get this message very often too.
This is very annoying.

All of my friends and acquaintances who use Opera, after auto-updating to the 25 version the Armenian letters turned to squares. It's horrible! Тhe worst thing is that the Opera developers have not paid attention to this topic.
Some people I've helped to solve the problem. But most Opera users in Armenia won't find the solution and will replace Opera with other browser.

I've also submitted a bug report 6 days ago.

The same problem is by me, opera shows squares instead of Armenian letters, the fonts in other languages have been also changed. This happened after opera's self-update to 25, I have changed encoding and fonts but nothing helped, any ideas else?

Open opera://flags/#disable-direct-write (paste this link to address bar) and in the "Disable DirectWrite" section press Enable button.

Have you tried disabling direct write on opera:flags?

It helped! Thanks.

I do not understand why it is activated by default, if it is an experimental feature?

Where did you get your nuOpera and was your 25 install a regular update?
What do other browsers show in your Windows 7?

I've downloaded the latest beta version from opera.com. Previous build has the same problem.

All other browsers (Opera 24, Opera 12, Firefox, IE11, Chrome) showing all Armenian letters normally. Only Opera beta 25 and Opera developer 26 displaying squares.

Here are some other screenshots (click for full size).

On the first screenshot there are squares after text "Armenian", but I would like to notice that some other languages in this list also displaying squares instead of native letters (Full list: Amharic, Armenian, Bengali, Georgian, Gujarati, Hebrew, Hindi, Kannada, Khmer, Lao, Malayalam, Marathi, Nepali, Oriya, Punjabi, Sinhala, Tamil, Telugu, Thai, Tigrinya.)

I've checked some of those links and they seemed ok here.in the sense of not being displaying squares.
My fonts are Time News Roman for Standard and Serif; Arial for Sans-serif and Consolas for Fixed-width. Default enconding is Western European (Iso 8859-1).

I have the same font and encoding configuration.
What is your operating system?
I'm using Windows 7.

Let me amend your link (using HTML):
Is this it?

Yes.

Could you paste the link to the page here? I've tried http://hy.wikipedia.org/ here and it seems ok.
Btw, it happens all the times? On all pages?

Here is the link http://hy.wikipedia.org/wiki/Օպերա_(դիտարկիչ)
It happens on most pages.
Here are some pages where problem exists: www.akumb.am www.yerevan.am/am/ www.1in.am www.edu.am www.itel.am/am/ facebook.com (with Armenian language) etc.
These pages showing correctly: news.am/arm/ www.lia.am/hy.htm

I've installed Opera 25 on another computer (I'm installing it with Stand-alone option, but I do not think that this matter) and here is the same problem.

Changing encoding (OMenu > Page > Encoding) makes any difference?

No. The Encoding is Unicode UTF-8 as it need to be. I've tried to change, but it does not help.

Is there the "Web-pages" section in your settings?
Try changing the fonts. I'm using DejaVu and Arial.

I have the same font configuration in Opera 25 as in 24. In 24 everything is normal with Armenian letters.