Going to https://ce.wikipedia.org/w/index.php?title=Малые_Угоны&action=edit&uselang=ce it does work as expected.
Going to https://ce.wikipedia.org/w/index.php?title=Малые_Угоны&action=edit it does not work as expected.

@Aklapper Are you sure? Those two pages look the same to me:

The second URL will use your account's interface preferences if set, it seems (or the content language if not); my account (set to en-gb) shows B/I, logged out shows Ж/К.

In T194211#4192308, @matmarex wrote:

@Aklapper Are you sure? Those two pages look the same to me

Yes, can still reproduce in Firefox 59 when being logged in. One loads https://ce.wikipedia.org/w/load.php?modules=oojs-ui.styles.icons-editing-styling&image=bold&format=rasterized&lang=ce&skin=vector&version=0jk8j11 , the other loads https://ce.wikipedia.org/w/load.php?modules=oojs-ui.styles.icons-editing-styling&image=bold&format=rasterized&lang=en&skin=vector&version=11h700j

In T194211#4193296, @Aklapper wrote:

Sorry, definitely my fault. https://ce.wikipedia.org/wiki/Белхан:ГӀирсаш was set to English language. Which means that nobody can reproduce the problem.

@Umar: What is the language setting in your account?

The Chechen language. And I see the Russian letter Ж.

@Umar: Let me ask you another time: Please always structure your bug reports like this in the future:

• Steps to reproduce
• What you expect to see
• What you actually see

I thought that the image above (F18085571) is what you expect to see. Obviously I was wrong. I don't speak Chechen. Having to guess what exactly is asked for in a bug report is not a good use of time.

This task has seven comments now. Still it is only you who knows which exact letter you expect to see, if Ж does not exist in Chechen language.

I suppose the expected behavior is an icon like this:
(this is a screenshot of WikiEditor toolbar with uselang=ce before it started using OOUI, at b0a5d572d1a4785ac520d0969ea1cf9bbb9a6523)

The custom icon for Chechen was previously added in rEWED38d28d5631d0: Add format-bold-Iab image for lang ce per T119716.

In T194211#4195536, @matmarex wrote:

The custom icon for Chechen was previously added in rEWED38d28d5631d0: Add format-bold-Iab image for lang ce per T119716.

I think it's better to make one letter. Like all wikis
https://commons.wikimedia.org/wiki/File:Toolbaricon_bold_I.png

@Umar: Please confirm that you have read and understood T194211#4194581 and that you will follow T194211#4194581 in the future. Thank you.

We made a discussion. And everyone voted for this icon https://commons.wikimedia.org/wiki/File:Toolbaricon_bold_I.png.

The page where discussed

https://ce.wikipedia.org/wiki/%D0%92%D0%B8%D0%BA%D0%B8%D0%BF%D0%B5%D0%B4%D0%B8:%D0%A4%D0%BE%D1%80%D1%83%D0%BC

The requested glyph would appears to be "Ӏ" which is CYRILLIC LETTER PALOCHKA (U+04C0).

We use sans-serif fonts for icons, but there appears to be an exception for italic-i, presumably because a sans-serif I is just not recognisable out of context.

Change 435819 had a related patch set uploaded (by Esanders; owner: Esanders):
[oojs/ui@master] Add bold icon for Chechen language

https://gerrit.wikimedia.org/r/435819

In T194211#4237177, @Esanders wrote:

The requested glyph would appears to be "Ӏ" which is CYRILLIC LETTER PALOCHKA (U+04C0).

We use sans-serif fonts for icons, but there appears to be an exception for italic-i, presumably because a sans-serif I is just not recognisable out of context.

Just use the Latin capital I instead of the palochka. It does not matter. Unfortunately, on the letter, a significant number of Chechens use the figure 1 in general.

Change 435819 merged by jenkins-bot:
[oojs/ui@master] Add bold icon for Chechen language

https://gerrit.wikimedia.org/r/435819

This change has been merged and is included in OOUI v0.27.1, which will be included in MediaWiki 1.32.0-wmf.7, which will be deployed to Wikimedia wikis next week, 5-7 May (per the usual schedule).

For reference, this is the icon we used:

(The same icon will be used by VisualEditor.)