Multi Language trailing slash in url

Question

I am currently using

RewriteCond %{REQUEST_URI} !^/system [NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+)/$ /$1 [R=301,L,QSA]

to remove trailing slashes in my urls, however for some reason it does not work with the multi language module - I'm using Expression Engine 2.9.0 and Multi Language 2.0.1

Example:

domain.co.uk/link/ > domain.co.uk/link (trailing slash is removed)
domain.co.uk/cy/link/ > domain.co.uk/cy/link/ (trailing slash is NOT removed)

I realise this is legacy software but I'm just trying to maintain this site.