Removing language slug from URL

Hello,

I am upgrading an old website to a newer version and of course started with latest version of WP and had to install all the plugins. The thing is that in the old version the translation of the site(it has only 2 languages – English(US) and Bulgarian, but there the languages are switched by adding a string at the end of the URL – http://www.xxx.com/?lang=bg or http://www.xxx.com/?lang=en.

But at the new installation the plugin uses http://www.xxx.com/ and http://www.xxx.com/bg/ and changing the URLs is not an option.

I have copied the settings of the plugin from the old website, but no effect.
I have tried everything suggested in the documentation, automatic translation is OFF, i have deleted all tables with extra translations to reset the plugin as per the support topic but still no result, I also browsed the forum topics and tried some solutions but nothing seemed to force the use of a string for the language instead of the slug added at the end of the URL.

Again – the result i need is the language to be set by the string and keep the URL single for both languages: f.ex.

http://www.website.com/?lang=bg and http://www.website.com/?lang=en
http://www.website.com/about/?lang=bg and http://www.website.com/about/?lang=en
http://www.website.com/contact/?lang=bg and http://www.website.com/contact/?lang=en
etc.

I would really appreciate you pointing me in some direction to resolve this.

Thanks in advance!

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