I'm curious why. Do users not know how to change the user interface language? Or did they learn how to use the computer from, say, an English reference and are now just accustomed to an English user interface?
As the most trivial example, software UI tends to use words that are short in English, e.g. "User" and "Account". In Russian these are typically translated as "Пользователь" and "Учетная запись", much longer than the original. Do your buttons stretch properly for such long words? Even if they are technically responsive to longer text, they still probably look weird.
Now imagine an on/off toggle that prints "On" or "off" inside itself. In Russian that is 8+ characters without abbreviation. If you stick with this design, you have to provide enough context to the translator so that they abbreviate translations to something sensible.
Speaking of context, "on" has quite a few different meanings in different cases. Does your translation pipeline support multiple translations for the same string? And do you provide the desired meaning to the translator?
And don't get me started on sentences. You can't compile a sentence "A B C" by providing separate translations for A, B, and C and then just slap them together. Grammar and sentence structure in other languages does not always match English.
Unfortunately translations for even AAA software often leave a lot to be desired, either stylistically, grammatically or semantically. It's a lot of effort to get it right.
I suspect it's partially because I'm much better at noticing bad $NATIVELANGUAGE than bad English.
So please, god, don't give me pages in Hungarian if at all possible even when I am visiting there. And at the same time could we just agree not to translate any of that? I speak if quite well, thanks much and Google Translate sucks horribly with an agglutinative language.
In Windows XP, Microsoft locked each license down to a subset of allowed languages based on the country the license was sold in. You can download a "Language Pack" for any language, but these only provide a half-assed superficial layer of support. A "Language Pack" only translates some aspects of the OS, falling short of being the equivalent to choosing that language as a native OS setting with the appropriate license.
A quick Google shows that "Language Packs" are still a thing in Windows 7, Vista, and 10. Perhaps they now offer complete support, or perhaps they are still a crippled aftermarket solution refusing to meet the expectations of any paying customer.
tldr; Many people in non-English countries are using Windows' licenses bought from English markets (such as the US). Even if these users know where to change the OS's language setting, odds are their native language isn't listed as an option.
The reason why power users generally prefer English is because many terms are poorly or awkwardly translated (and some of those translations are historical, and are not going to change now); because English is often shorter, making the UI more compact / neater; because it's easier to find instructions, error messages etc on Google; or because they're developers, and they work in English most of the time anyway, and don't want the unnecessary overhead of dealing with two languages on the screen (I assume there are other fields in which English similarly dominates, but this is the one that I know from personal experience).
There were some English keywords in there that I googled, but when I clicked on a link that looked promising, Microsoft decided to show me the German version of that page instead.
Translating the instructions for changing the settings was fun and frustrating at the same time, especially since the menu organization was subtly different between the German and Chinese localizations.
A lot of software gets poorly translated. And worse: A lot doesn't get translated, but relies partly on the interface language of the OS. You get horrors in the pattern of "Would you like to answer this question? Ja/Nej".
Windows up to and including 3.11 in my local flavour (Danish), I could deliberately crash from various selection boxes, because someone hadn't bothered to think the translation procecess through.
Being in a tech job, when resolving issues with interface with international user base, taking screenshots in english, for example, has the most far-reaching benefit. More people can understand it.
Also many companies (including Microsoft) have poor translations. Using English interface bypass this issue.
Aside from that, like many others I also find the English interfaces to be far superior in quality to localized interfaces which will often have errors in their translation. Furthermore some choices of words in translations just look plain dumb to me even though they are correct.
So if you mail a Dutch person a CSV file that follows RFC 4180, chances are they can't open it properly because of Excel. A surprisingly large number of otherwise capable people get stuck at this point.
(OpenOffice/LibreOffice is smart enough to recognise tabulated data when it sees it, and will simply present you with the import screen for tabulated data with its helpful live preview of the columns.)
So when I had to use Excel all the formulas were named in Norwegian.
I downloaded a portable version of LibreOffice but that triggered the anti-virus :I
Sometimes I would use Google Docs instead but for company confidential information I obviously won't upload that data to Google so then I'm stuck with Excel. Even for non-critical data Google Docs might not be an option simply because you are working on the file together with someone else who is using Excel and constantly uploading and downloading the file would be annoying, as well as the risk of Google Docs not supporting 100% of the features of Excel leading to complicated spreadsheets getting mangled. (Same problem with using LibreOffice to work with someone using Microsoft Office.)
Also, the material found on the web for that software (help, tutorials, etc.) also come in English as well. Trivial example: in multiplayer games knowing the English name for items, locations etc. helps with communication with other players.
So I tend to set the interface to English even when it is auto-detected correctly.
One is that I started using computers before any mainstream software was available in Latvian, so I am used to English being the language of all computers.
Another major reason is the translations themselves, which take two dramatically different approaches. There are official Latvian translations for computer terms, as suggested by the language academy. These translated terms are very much "designed" - they're decided on at committee meetings and, while linguistically sound, I find many of them very unnatural, and their meaning impossible to guess without learning the term explicitly. I won't bother with examples here as there's probably no Latvian speaker reading this anyway. So using those official terms is one approach, and it's followed by, for instance, Microsoft. The other approach (used by most open-source localizations) uses more natural vocabulary with more English borrowings, and only some of the academically-defined terms. Even if I wanted to use Latvian UIs, I would constantly be looking at two fairly different sets of vocabulary.
Of course the translations themselves are also poor and often incomplete, unsurprising for such a small language. Some programs automatically show up in Latvian after installation (thanks to, once again, bad use of regional settings), and I will usually see a Latvian/English mix right away because much of the text isn't translated. I've had the misfortune of briefly using the Latvian UI for Windows XP, and it was full of typos and inconsistencies.
But above all, by now it's just a matter of habit. I am as comfortable in English as in my native language, and would have no incentive to use a non-English UI even given a perfect translation.
I have quite the opposite experience.
1. In Taiwan and Japan, phones and pc comes correctly configured UI language for us. But I switch it to English anyway.
2. UI Language is usually not something people can just try to use and "get by". Languages are almost always immediately switched user's prefered one upon recieving product in my experience.
These days the textual UI of the browser isn't too important (the icons are what matter for day to day usage) so people just live with it.