Language not changing for plugin


This plugin dos not use my language on strings, I know it should. I have checket with Your site, and the strings I want to use are translated. (24 %)

I just need a few lines in my own language, like when people sign up for "Subscribtion" says "Thanks.....and email has been send ..etc..

I might have installed the WP in English, but now I have changed it to my own language.

How and when will the plugin follow ??

Do I have to un install and reinstall the plugin?