Good UX means including translations for supported languages, not telling the user "do it yourself by highlighting content".
Not translating entire articles to a language you don't support has the easy remedy of letting people select the text and use third party tools to support their specific use-cases. But not including translations for your clickable content for languages that aren't supported are the literal practical limits of ability. I would rather my apps work for people in languages I do support, with full accessibility (and minimal scripting overhead), than to have them work poorly for keyboard-only users in all languages, regardless of my app's support for them.
Again, we're talking about the stuff that should be iconic. Things that can literally be represented by icons. Buttons and tab headings. Things that you shouldn't actually need translated AT ALL, much less into every single language there is.
Even when the language is supported I have had GDPR popups block that language selection. The text in the popup was also not selectable which made it very hard to read what I was or was not agreeing to.
I know you're not asking me, but I would really love the "copy" feature added to ALL context menus.
Right clicking a standard anchor element gives you the "copy link" option, but you don't get to copy the word without having it selected. Would be nice to just have a "copy word" feature, for starters. Could even be expanded so that it auto-selects the text after copying it so that if you wanted to copy more than just one word, you could expand the highlight (with the little widgets on mobile, or with keyboard/mouse selection in that one state on desktop) and then get a "copy text" option that copies all of the selected content.
