Remove English USA

I want English UK not English USA on my LibreOffice. How can I achieve this.
I have set English UK but English USA always appears.

You can select the official English (GB) installer from this page.

Do you refer to the UI language or to the document language?

For the UI language: install the corresponding language pack. How to do that depends on your operative system, so please, edit your original question to add more information.

For the document language: open a new document, bring the style editor on front with F11 and modify the paragraph style called Default Style in order to change, in the Font tab, the language. Then, go to File → Templates → Save Template, provide a name for the template, check the Set as default template box, and click on Save.

I don’t think you can remove English USA because it comes bundled with the basic LO configuration. Other variants of English must be added with a language pack, which you seem to have done.

To switch default language permanently, go to Tools>Options, Language Settings>Languages. In Default Languages for Documents (Western), select English (UK). If this item is not flagged with a check marck under ABC, then you did not install the English language pack. Do that first.

To verify your setting has been taken into account, open the style side-pane with F11, right-click on Default Style for Mofidy and go to Font. The Language drop-down menu should display English (UK).

Of course, if you forced a different language on some other style (they all inherit from Default Style), this choice overrides the language from Default Style.

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EDIT

Your question did not mention if your locale is English or some other language. In case it is English, are you en_UK or en_US?

If your locale meets your requirement for English (UK), you can choose in Tools>Options, Language Settings>Languages Default - <your_language (your_country)> which has the advantage to be in sync with OS configuration.

Thank you! This has worked. My locale is South Africa. We still have grammar that has gone missing in English US.

Strange that English US can be default as this is not a language. It is a dialect with far less grammar and too tiny vocabulary.
I do not want the US dialect on my computer, but really like the office. Should be possible to get completely rid of.

We develop a very complex program. The program needs to communicate to people- show UI, messages, errors…, even without any localization files installed at all (or they malfunction) - if not for users, then for us developers (but users also may benefit from that in some corner cases). That leads to a natural decision, that some language must be compiled into the core of the program - not because it’s “important”, but because it’s convenient and has significant upsides. Then it would be natural, that that language is the one that is used by developers for communication in the project. In this project, it is English (not “US” or “UK”, but simply some kind of “international” English, allowing to people from Germany, China, Finland, Ukraine, Russia, Spain, India, etc., etc., to understand each other).

It is the convention that that will be the en-US. And it means, that the most “incorrect” text gets compiled into the core as “en-US” - because the strings of that “translation” are created initially not by some linguists, but by programmers, who usually speak on it not as their native. Then it, of course, will be polished a bit … but you - as such a person who can want to eliminate with strong emotions, having some prejudice to a language spoken by hundreds of millions, and desire “get rid of” a language from their system (wow, I’m glad I don’t know you in person), you may be glad, that your preferred translation is being created by people who specifically look and think how to properly call this or that, or translate this help page, to your language / variant.

And no, we won’t consider changing the workflow, just to please someone’s unreasonable emotional attitude.

Then happy Mike kaganski that does not know me, unusually sensitive and delicate Mike (from Monsters Inc?)
solution is easy.
Know who you want.
And I am out of here.