Hi kaftakis
My sincerest apologies for only getting back to you now.
These strings can be changed by going to 'Settings' under 'Newsletters' and clicking on the 'Subscribe Widget' tab.
Unfortunately you wont be able to use language 'switching' as such as our plugin does not have the functionality to do this with WPML for example. We have plans on building this in, in the future though.
Kind Regards,
Jarryd