Synonyms for different languages in LibreOffice Writer? [duplicate]

I have been trying to use English-UK thesaurus in LibreOffice but so far cannot get it to work. I have installed mythes-en-us as only it was available in repos. As suggested in some forums I searched for openoffice.org thesaurus, but again US version was available. As a result I can't enable thesaurus when I choose English UK:

As instructed elsewhere I tried this:

cd /usr/share/myspell/dicts
sudo ln -s th_en_US_v2.dat th_en_GB_v2.dat
sudo ln -s th_en_US_v2.idx th_en_GB_v2.idx

Still the result is same as shown in above screenshots.

What can be done now?

Here's what worked for me. I found most of these steps in this blog post, credit to the author for figuring this out.

1. Download the spelling/hyphen/thesaurus dictionaries you want from LibreOffice's extensions download page.
2. Install them in LibreOffice Tools -> Extension Manager -> Add and then close LibreOffice.
3. sudo apt-get install libmythes-1.2-0 hunspell
4. sudo apt-get install mythes-en-us hunspell-en-us
5. cd /usr/share/mythes/
6. sudo ln -s th_en_US_v2.idx th_en_GB_v2.idx
7. sudo ln -s th_en_US_v2.dat th_en_GB_v2.dat
8. Open LibreOffice Writer and go to Tools -> Options -> Language Settings -> Writing Aids.
9. Verify the new thesaurus is selected, then from Writer test it by pressing Ctrl + F7 to bring up the thesaurus dialogue.

This latest version of the Libreoffice Extension "English Dictionaries" works with the latest version of Libreoffice and will hopefully get the thesaurus activated for you.

http://extensions.libreoffice.org/extension-center/english-dictionaries

With each installation of Libreoffice on any of the Distros I have installed for myself or others I have found that the thesaurus always works after I have installed the English dictionaries for Apache OpenOffice-2013.07.31 rather than any extension from LibreOffice.

This makes all the above solutions unnecessary.

This OpenOffice dictionary extension is a year old now and although there are more recent versions here English dictionaries for Apache OpenOffice they always give the error

Extension requires at least OpenOffice.org reference version 4.0

when I attempt to install them.

• For English-UK, the correct answer is in Mik's

I am posting this answer for other locales:

So:

• For French, go here to get the French dictionary and install in LibreOffice Writer in Tools-Extensions manager. (The spelling works before installing that, but synonyms context menu does not).