I tried to make translation of this plugin as easy as possible for everyone.
Simply go to locales directory and make a copy of any existing translation file. Rename it to code of the language you will translate to. Refer to http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes (639-1 column) for code you should use for your language.
Now open this new file in your favourite text editor and translate strings.

First, there is $spr_locale_language="some_language_here"; You should replace some_language_here with name of your language in that language. This will show up as name of localization on settings page.

Current values should give you an idea of where that string is ussed.
Please, don't touch anything which looks like key_here in $spr_localization['key_here']. It's the thing that allows plugin to find needed translation for a string so if you change that, plugin will not be able to find needed key and default value will be used.
What you want to translate are strings in "" after $spr_localization['key_here']="Some string which you want to translate"

Keymap:
Strings which have keys starting with settings_ belong to the settings page of plugin
Strings which have keys starting with widgets_ belong to widgets and meta boxes
Strings which have keys starting with errors_ belong to error messages
Strings which have keys starting with vote_counter_ belong to vote counter

Basically, if you just want to translate things that can be seen by users and guests, you only need to translate strings with keys which start with vote_counter_ and errors_ and can leave everything else as it is (Please, do not delete any of strings in the file)

As of now, there are 2 special cases to singular/plurar forms of vote counter:
First applies to numbers ending with 2,3 or 4 but not 12,13,14. Examples: 22, 153, 1004.
Second applies to numbers ending with 1 but not 11. Examples: 51, 121, 1001.
Do NOT delete them even if they're not special cases in your language. Simply translate them with fitting singular/plural form.
Likewise, if your language got special cases in which different form should be used, please let me know and I will update plugin to properly handle them. 

Important: If things broke after you selected your translation in settings (there are various reasons for this, like missing " or ; etc), there is no need to panic. Simply rename your translation file to something else. This way, plugin will use default values (English) which will "un-break" things, allowing you to fix your translation file. When you're done with fixing, simply rename file back to the old name.