All in game text is contained in a single file, the English.str file (language name maybe different if you have a different language version of the game). Simply copy that file, open it an notepad, and translate everything between the parenthesis on lines with Value "   ". You can then make a language mod with that modified file.

Just curious, what language you are wanting to translate it to? I know there are either official or unofficial translations of at least French, German, Japanese, and possibly Spanish, Turkish and Chinese.

That is correct. Most modders will usually put all of their additions at the beginning or end of the file, so if you have the base game translated already that should save you a lot of work since you only need to translate the new strings. If you're unsure you might want to ask the creator of Maelstrom directly, he's a pretty cool guy.

Also, for Russian I assume you'll need to manually save the file as unicode, by default English.str is in ASCII.