XOOPS Version XOOPS 2.5.7.2
PHP Version 5.4.45
mySQL Version 5.5.54

As xLanguage doesn't work I wonder if I can make a duplicate install of XOOPS 2.5.7.2 in a subdirectory in the language I want and reinstall all the modules and recreate all the content in the language I want

(i.e. rfu.in.ua english and rfu.in.ua/ua/ ukrainian)

I tried it on my localhost but there seemed to be a cache problem and the languages weren't showing properly.

xLanguage works.
I don't know why it doesn't work for you but it works.

Not on my site it doesn't

And I paid a lot of money to have the core and all those modules translated too