I can confirm that there is definitely a problem with SmarterTrack 12 and those localizations:
Under "Language and Locale" - "Supported Languages" I have solely configured the language "German" with the locale "German (Germany)". It is the "Default language" and "Enable language for users" is checked.
I did a small change on the corresponding language file "de.xml" and after storing that file back on the server I have lost the localization and the complete website defaults to "English".
In the management interface under "Language and Locale" - "Supported Languages" the field "Language Pack Installed" is no longer checked although I can still choose the German language in the frontend.
I should note that I did many changes to the language file throughout the last days and I have seen this behaviour only twice before. In both cases I was able to come back to the German language file by installing some other "Default language" under "Language and Locale" - "Supported Languages" and switching back to "German" afterwards.
This time I have simply saved the language file "de.xml" without any changes once again and suddenly the field "Language Pack Installed" was checked again and the website showed the German texts.
An additional hint for @hamed: Please make sure that your help file is XML validated! I once had a small syntax error in my language file and suddenly 40% of my translated strings were gone!