Translation issue

Hello,
I am French and I use your plugin on 2 sites in premium version. I can’t translate certain plugin texts with loco translate or PoEdit

– Shipping
– price
– Enter your promo code
– item added

I had succeeded on the 1st site but it seems that the solution I found was not effective in the long term.

I also tried with the solution you give on this page: http://docs.xootix.com/side-cart-for-woocommerce/#translation
But it doesn’t work for me.

Do you have another solution to give me?
In PHP can be?