Plugin subscribe-to-comments problem

I recently came across the Subscribe to Comments 2.1 plugin and attempted to translate it to German. After uploading and activating it I noticed that I missed some of the English text and so I adjusted it accordingly. But after uploading the new version of subscribe-to-comments.php the OLD text still showed. In fact, no matter how many times I change the text and re-upload the file it always shows the text the way it was in the very first version I uploaded.

Why is that? Does anyone know how I can fix this? (Deactivating, deleting, re-uploading and activating the plugin doesn’t work.) Any help is greatly appreciated.