Wordpress plugin offers many ways for detecting language users are selecting. You can use different approach for language detection:
This is simple way of seeing what local was selected, and it shows up as query parameter in URL
This is not recommended, and it is not SEO friendly. This option works by default with plain WordPress permalink.
This is one of the recommended ways to detect local for the website, this option is SEO friendly, but requires small updated with WordPress Permalink.
adds /en/ in front of URL
It will not work with Plain WordPress permalink. Navigate to Permalink settings:
Settings -> Permalinks
you can select any permalinks but remove index.php if it shows up as part of permalinks, or you can create custom structure.
Sometimes Language detection is done with subdomain:
For this option, additional changes to DNS subdomain record and Wordpress redirection should be completed.
Translation Exchange plugin will detect subdomain and present the page in selected locale