Which can also be understood in most of ex-YU, so: Croatia, Bosnia & Hercegovina, Montenegro, Serbia, Kosovo...just let me know & mail me a form to translate!
Great, you already have everything you need.
Go to C:\Program Files\eFMer\TThrottle\lang
Open languages.xml with a simple text editor like the build in notepad.
I personally like notepad++ https://notepad-plus-plus.org/
Add you language tag to this file like this
<Name>new in your own language</Name>
<Id>1033 this number is shown in the TThrottle log: Language: User: </Id>
Now copy TThrottle_ENU.ttlang to TThrottle_HRV.ttlang
HRV depends on the 4 digit number probably something from this list: http://www.the-localization-tool.com/language-codes-mfc/
If you got it wrong, you will get an error message about a missing file with the correct name.